Insect Pests of Rainfed Wetland Rice

Insect pests of rainfed wetland rice in the Philippines: population densities, yield loss, and insecticide

management

J.A. Litsingera*, B.L. Canapib, J.P. Bandongb, M.D. Lumabanb, F.D. Raymundoc and A.T. Barrionc

a1365 Jacobs Place, Dixon, CA 95620, USA; bInternational Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines;cPhilippine Rice Research Institute (PhilRice), Maligaya, Science City of Munoz, Nueva Ecija 3119, Philippines

(Received 21 June 2008; final version received 13 January 2009)

Rainfed wetland rice (RWR) had more species in common with irrigated wetland than dryland rice agroecosystems.Across ecosystems, higher pest densities and losses were recorded in RWR sites. We hypothesise that under lowpressure from natural enemies, vegetative stage losses became particularly high due the combination of whorl maggotand caseworm damage combined with the physiological stress of transplanting shock. Both of these pest groupsbenefited from an expanded vegetative period common in RWR agroecosystems. Losses in older rice were probablydue to stemborers. RWR is more prone to an array of physiological stresses than irrigated rice that we believeminimises crop compensation to accentuate insect losses. Chemical control is uneconomical mainly due to the lowyield potential of RWR and the poor efficacy of applied insecticide.

Keywords: rice insect pests; yield loss; natural enemies; action thresholds; chemical control; crop compensation; cropstresses; integrated pest management

1. Introduction

Domesticated rice (Oryza sativa L.) probably evolvedfirst as a perennial, terrestrial species which then becameadapted to an aquatic existence in rainfed wetland rice(RWR) ecosystems (Catling 1992). RWR is the tradi-tional system of wetland rice culture where farmersutilise accumulated rainfall to puddle the soil to enablehand transplanting. RWR is normally a single rice cropgrown in the rainy season, thereafter fields are either leftfallow or sown to a drought-tolerant, short-maturing,non-rice crop over the dry season. Due to irregularrainfall, rice bunds tend to be tall as farmers attempt tostore large amounts of water after transplanting. Threemain rice agroecosystems developed from the RWRcultural archetype to reach most habitats within awatershed (Garrity et al. 1986): (1) deepwater rice whichoccupies large river floodplains where ponding exceeds1.5 m for more than a month, (2) dryland rice, located inthe uppermost landforms where rice is dry-seededwithout ponding in non-puddled soils, and (3) irrigatedrice which is the most recent agroecosystem replacingRWR in the more favourable landforms near sources ofwater. Irrigated rice greatly expanded after the advent ofthe Green Revolution modern rices in the late 1960s(IRRI 1985a).

RWR covers about 38 million ha, representing 28%of rice area worldwide (Garrity et al. 1986). Approxi-mately two-thirds of the total RWR environment isunfavourable insofar as frequent drought, submer-gence, and adverse soils contribute to low yields.

Farmers often hedge their bets by having fields in bothlow- and high-lying locations in a toposequence (landfragmentation) to increase the probability of a harvestin any rainfall contingency (Fujisaka 1990).

The RWR plant archetype is attuned to the Asianmonsoon climate. Cultivars are tall (1–1.5 m) totolerate flooding but have less tillering ability (DeDatta1981). They are photoperiod-sensitive and long-maturing thus have more time to compensate frombiotic and abiotic stresses, a trait that ensures stableyields. While transplanting may last for over 3 monthsto cover all field locations, flowering and crop maturitybecome synchronised by the short day lengths thatoccur at the end of the monsoon season. Thus, the cropmatures in dry weather to provide optimal grainquality. Unfortunately production by the low yieldingtraditional RWR cultivars is insufficient to feed therice-eating world, a dilemma which motivated thedevelopment of modern, high-yielding, semi-dwarfs.

There are few entomological research papers thatrelate specifically to the RWR ecosystem. Mainly listsof pests, prioritised by importance in most Asiancountries, have been compiled (Litsinger 1979; Mackill1986; Heinrichs et al. 1986; Kalode et al. 1986).Farmers in Thailand, Cambodia, Laos, and Nepalidentified key insect pests, along with control practicesthat generally included cultural methods and botanicalpesticides (Fujisaka 1990).

The Philippines has 1.2 million ha of RWR whichrepresents 40% of its rice area (Garrity et al. 1986).

*Corresponding author. Email: [email protected]

International Journal of Pest ManagementVol. 55, No. 3, July–September 2009, 221–242

ISSN 0967-0874 print/ISSN 1366-5863 online

� 2009 Taylor & Francis

DOI: 10.1080/09670870902745070

http://www.informaworld.com

Generally, RWR farmers use fewer agroinputs thanirrigated rice farmers, particularly in unfavourablehabitats (Fujisaka 1990). Surveys of RWR farmers inIloilo and Pangasinan provinces in the late 1970s,representing favourable and unfavourable RWR sites,revealed that 54 and 29% used insecticides averaging2.5 and 1.3 applications per crop among users(Litsinger et al. 1980b). In Cagayan province, 47% offarmers used insecticides, averaging 1.9 applicationsamong users (range 1–4) (Litsinger et al. 1982).Another survey in Central Luzon, also in a favourablesite by Pineda et al. (1984), noted that RWR farmersadopted insecticides at a slower rate than nearbyirrigated farmers, but lagging some 5 years behind.Indeed the adoption rate slope mirrored that ofirrigated farmers where 70% of both groups usedinsecticides averaging 3–4 applications each amongusers. Farmers will spray upon seeing some mothsflying when flushed from the fields or by observingdamage only on a few hills (Bandong et al. 2002). Thesurveys also revealed that farmers severely underdosedat about half of the recommended rates.

The current study was carried out by a joint projectbetween the International Rice Research Institute(IRRI) and the Philippine Department of Agriculturethat formed multi-disciplinary teams at three RWRsites (Morris et al. 1986). The task was to increase riceproduction by boosting cropping intensity via repla-cing traditional rices with modern photoperiod-insen-sitive ones that mature within 4 months. The teamstested different cropping patterns and managementpractices with a view to optimise input usage. RWRenvironments are classified as favourable or unfavour-able (Garrity et al. 1986). The latter are under chronicdrought stress and subjected to submergence atdepths 450 cm for several days which is representedby Cagayan province. Sites in Iloilo and Pangasinanprovinces were favourable, as submergence anddrought were less frequent and enduring. In thesesites, double-cropped rice was feasible using earlymaturing rices and direct-seeding methods, while inCagayan we tested growing mungbean before rice aswell as early planted, direct seeded rice designed toescape anticipated flooding later in the season.

We documented the arthropod fauna and quanti-fied yield loss using the insecticide check method. Asinsecticide had already been adopted by farmers, ourobjective was to rationalise usage by testing actionthresholds as decision tools (Litsinger et al. 2005).Testing of the different cropping patterns allowedecological information to be gathered on the interac-tion of cropping patterns and site on insect pestabundance. Rainfall patterns also differed each year,introducing yet another dimension of insect pestecology. Results are compared to Philippine drylandand irrigated rice ecosystems managed by similarapplied research teams. The former has mainly soiland seed pests, uncommon in wetland culture, while

the latter has a history of pest epidemics leading tosevere losses. Parasitism levels over a range of RWRpests and stages was also measured. A more thoroughinvestigation in RWR ecosystems which historicallyhave been less affected by pest epidemics may lead toinsights that may aid in the management of more pest-prone, rice ecosystems.

2. Methods and materials

2.1. Study sites

On-farm research was carried out for 3–5 years in eachof three sites where comparisons were made in similarlyoperated dryland and irrigated sites (four sites each)spanning a 15-year period 1976–1991.

2.1.1. Iloilo province

Iloilo averaged 1.5 m/year rainfall during the studyperiod 1976–1979 (Morris et al. 1986). The slopingterrain predisposed the watershed to drought. Theprincipal land forms in Oton and Tigbauan towns weresideslopes, plateaus, and low plains. RWR occurred ina parallel strip along the coast sandwiched betweenuplands and rice lands irrigated from small rivers.There was no second rice crop before the project, butindeterminate cowpea was commonly relay-sownbefore the single rice crop harvest.

2.1.2. Pangasinan province

Manaoag, Pangasinan in NW Luzon, is a large, low-lying, rice bowl with a high water table and was subjectto submergence after heavy rains. Rainfall averaged1.7 m/year during the study 1976–1980 (Morris et al.1986). Mungbean was broadcast-sown after riceharvest in tilled fields. Farmers alternated betweendeep ponding and draining their fields to cope with adual micro-nutrient problem of zinc deficiency and irontoxicity. Less field water led to weediness andexacerbated drought stress. The project introducedzinc application so that farmers no longer had to draintheir fields. More detailed site descriptions for theIloilo and Pangasinan sites can be found in IRRI(1976, 1977, 1980a).

2.1.3. Cagayan province

The third site was Solana located in Cagayan provincein NE Luzon where annual rainfall from 1980 to 1982averaged 1.8 m. Rice lands lie along sloping terracesformed by the Cagayan river but too high to receiveirrigation. Some farmers store canoes under theirhomes because, due to deforestation in the upperwatershed, flooding is common during the frequenttyphoons. On the well-drained upper wetland slopes,some farmers plant mungbean at the beginning of therainy season; otherwise, no other non-rice crops are

222 J.A. Litsinger et al.

grown in the rice fields. Maize is commonly grown inthe adjacent uplands. The nearest irrigated rice was20 km away in Gadu. Further site description can befound in IRRI (1981a).

2.2. Research teams

Field offices were established in each site. Localassistants acquainted with the farmers and fluent inthe regional languages were recruited. This gave thelocal teams acceptance in the target farm communities.The annual on-farm research programme was con-ducted by multi-disciplinary teams with researchersspecialising in varietal testing, agronomic practices,weed control, plant pathology, and economics as wellas entomology. Laboratory assistants were trained inrice arthropod identification and each was equippedwith a dissecting microscope.

2.3. Rice crop management

All trials were superimposed on farmers’ fieldsmanaged under the teams’ agronomic recommenda-tions carried out by the farmers with the exception ofinsect pest control practices. Because the projectinvolved introducing modern rices into these areasthat were responsive to better management, agroinputlevels were being tested at levels above those used byfarmers on traditional varieties. Farmers immediatelybegan adopting the improved varieties in the favour-able sites along with increased use of inorganicfertiliser usage. Almost no farmer adopted the researchteams’ action thresholds, however, as this wouldrequire specialised extension programmes which didnot materialise. Trials with traditional varieties weremanaged under the farmers’ low input systems. InIloilo and Pangasinan, rice variety IR28 was first testedand then replaced with IR36; both are early-maturing,modern semi-dwarfs (105–110 days). In Cagayan, IR36was first tested and then replaced by IR52, a 116-dayvariety with some drought tolerance. All three ricevarieties were resistant to rice green leafhopperNephotettix virescens (Distant), while IR36 and IR52were also resistant to rice brown planthopper Nilapar-vata lugens (Stal). The major traditional variety inPangasinan and Cagayan was Wagwag. In Pangasinanit was Inano while BE3 and Kapopy dominated inIloilo. Except the wet-seeded first-crop fields in thedouble rice crop pattern, all crops were transplanted.The seeding rate for transplanted rice was 30 kg/haand 100 kg/ha for wet-seeded rice which was soakedfor 2 days before being broadcasted on puddled soil.Only inorganic fertiliser was used with NPK rates(kg/ha) of 70-40-0 in Iloilo, 80-0-0 in Pangasinan, and30-0-0 in Cagayan. In Pangasinan, zinc oxide wasapplied at 25 kg/ha to wet-seeded rice and by seedlingroot dip if transplanted. Weeds were controlled by acombination of ponding, herbicides, and hand

weeding. Grain yield involved five 5-m2 samples takenin a stratified grid within each 100–200-m2 plot. Grainwas dried to 14% moisture content.

The site teams were encouraged to interact withfarmers to improve on current insect control practices.This farming systems approach involved an annualupdating of recommended farming practices based onthe results of each year’s on-farm trials (Zandstra et al.1981). For insect control this meant improving theaction thresholds and choice of insecticide. Improvedpractices included identification of better varieties, moreefficient inorganic fertilisers, and improved weed andinsect control. All things being equal, the improvedpractices would have steadily increased yields with theconsequence of increasingly augmenting the crops’ability to compensate from insect pest damage with aresulting increased lowering of measured yield losses.Sites in the other two rice agro-ecosystems underwentthis applied research process. The results did not showthis trend, however, due to the more powerful randomweather events on yield common in the sites. This will beelaborated more in the discussion section.

2.4. Treatment descriptions

2.4.1. Partitioned-growth-stage yield loss trials

The yield loss trials involved five treatments employingthe insecticide check method (Litsinger 1991). Threecrop stages were recognised: (1) vegetative (transplant-ing to panicle initiation), (2) reproductive (panicleinitiation to flowering), and (3) ripening (flowering tomaturity 10 days before harvest) (Yoshida 1981). In atypical 110-day modern variety, the reproductive stagebegins about 40 days after transplanting (DT) and endsabout 30 days later. In traditional rices only thevegetative stage is prolonged.

The seedbed had been included in experiments priorto the current study, but as no significant yield loss wasever measured (Litsinger 2009), this portion of thevegetative growth stage was eliminated from experi-mentation. The first treatment termed ‘full protection’attempts to achieve the crop’s yield potential with theleast possible amount of insect damage. Weeklyinsecticide sprays at the manufacturers’ recommendeddosages were applied to each plot with inter-plot spraydrift minimised by a mosquito cloth-covered 1 6 3 mwood frame held downwind by two assistants. In-secticides (monocrotophos, chlorpyrifos, or g-BHCsprayed every 10 days at 0.75 kg a.i./ha each in therespective three rice growth stages) were selected forefficacy as well as proven phytotoxic or phytotonicneutrality (Venugopal and Litsinger 1984). The in-secticides were applied at 300–500 l/ha spray volume(increased with crop growth) with 19-l, lever-operated,knapsack sprayers fitted with hollow cone nozzles.From the second to fourth treatments, insecticide waswithheld from each successive growth stage; the fifthtreatment was the untreated check.

International Journal of Pest Management 223

All treatments were arranged in randomisedcomplete block design (Litsinger et al. 1980a). Withineach co-operator’s field (replication), a 0.2-ha researcharea was demarcated with plastic string tied to bamboostakes. Plot sizes were 100–200 m2. Side by sideplacement of insecticide treated and untreated plotshad been found to have unbiased effects on pestabundance (Litsinger et al. 1987b); total yield loss,calculated both in terms of grain weight and percen-tage, was the difference between the ‘full protection’and untreated check. To calculate percentage, total losswas divided by the full protection yield. The losses inthe three separate growth-stage omission treatmentswere calculated as the respective differences from thefull protection plot. These were summed and adjustedupwards or downwards proportionally so that the totalequalled the total yield loss in each crop.

2.4.2. Chemical control treatments

Two types of insecticide control practice were rando-mised among the yield loss plots in the superimposedtrials, so as to generate recommendations for farmers.Their inclusion each season followed an iterativeprocess of technology development for each site. Thesetreatments included: (1) the use of action thresholds asa guide to insecticide application and (2) a prophylacticinsecticide regime. An action threshold is composed ofthe pest character to be measured as well as thetriggering level of abundance and an insecticideresponse at a specified dosage. The action thresholdpractices were reviewed each year and changed ifthe trials pointed to a better practice (Table 1). Theprophylactic treatment involved soil incorporation of0.5 kg a.i. carbofuran granules/ha before transplantingfollowed by two foliar sprays of 0.4 kg a.i. chlorpyr-ifos/ha 10 days apart during the late reproductive stageto prevent stemborer damage. This practice wasbased on the results of earlier studies that showed

yield losses were greatest in the vegetative stage andthat stemborer whiteheads were often high. Moretimely application occurred via prophylactic applica-tions than from monitoring which may provide bettercontrol. Soil incorporation of low dosage carbofurangranules had been found to be highly effective (delaCruz et al. 1981).

Crops were monitored weekly, and when a thresh-old was reached the currently recommended insecticidewas applied within a day. Insecticide technology wasalso developed in an iterative process; thus if efficacywas low, adjustments were made, normally involving achange in the character, chemical, or dosage. Tests todetermine the minimum effective dosage were under-taken in separate on-farm trials with a view to costsaving (IRRI 1985b). Foliar sprays were applied asdescribed in the yield loss trials. The degree of controlwas based on comparisons between the full protectionand the untreated check in the insecticide checktreatments.

Cost and return economic analyses were carried outfor each treatment that led to a significant yieldincrease. The protocol of Smith et al. (1988) wasfollowed based on 1986 prices for insecticides, unmilledrice, and labour. Interest on materials was levied at60% per season, spraying labour was set at 8 h, andgranular application at 4 h/ha. The 60% interestcharged was a realistic rate for rural Philippines andlabour costs/ha were assessed 33% interest. Pestmonitoring was assessed at 60 h/ha per season for theaction threshold treatment.

2.5. Arthropod sampling methods

Pests were sampled weekly in the action threshold,prophylactic, and untreated check plots, but only onceper growth stage in the other yield loss treatments. Thetotal number of tillers and leaves per hill was recordedalong with the percent damaged by whorl maggot

Table 1. The evolution of action thresholds for rainfed wetland rice insect pests in the Philippines, 1976–83.1

Growth stage Pest Year

Action threshold2

Character Insecticide (dosage kg ai/ha) Cost ($/ha)

Vegetative Whorl maggot 1976 25% damaged leaves monocrotophos EC (0.75) 231982 15% damaged leaves triazophos EC (0.40) 12

Caseworm 1976 15% defoliation monocrotophos EC (0.75) 231982 10% cut leaves malathion EC (0.40) 3

Stemborer 1976 10% deadhearts monocrotophos EC (0.75) 231982 15% deadhearts chlorpyrifos EC (0.40) 7

Reproductive Stemborer 1976 3% deadhearts monocrotophos EC (0.75) 231982 5% deadhearts chlorpyrifos EC (0.40) 7

Leaffolder 1976 10% damaged leaves monocrotophos EC (0.75) 231982 15% damaged flag leaves BPMC WP (0.40) 6

Ripening Rice seed bug 1976 4 bugs/m2 monocrotophos EC (0.75) 231982 8 bugs/m2 diazinon EC (0.40) 7

1Action thresholds were re-evaluated each year in an iterative process based on field results. Only the beginning and final thresholds are shown.2EC ¼ emulsifiable concentrate (liquid), WP ¼ wettable powder.


Hydrellia philippina Ferino and various defoliators at 21DT or 35 days after sowing (wet seeded crops). Damagecaused by each of the four common defoliating insectpest species [caseworm Nymphula depunctalis (Guenee),armyworm Mythimna separata (Walker)/cutwormsSpodoptera spp., green semilooper Naranga aenescensMoore, and green hairy caterpillar Rivula atimeta(Swinhoe)] could be readily distinguished. Stemborerlarvae feed internally in tillers, severing vascular tissueand so causing wilting which is distinguished on youngertillers as ‘deadhearts’ and in panicles as ‘whiteheads’.Stemborer-damaged tillers/panicles were pulled to con-firm that larval feeding was responsible. Deadhearts andwhiteheads were sampled during tiller elongation andripening stages. Leaffolder larvae fold the leaves in adistinctive fashion. Damage was recorded in the flag leafstage, the most important period in terms of yield loss(Heong 1990). Rice seed bug adults and nymphs weresampled by visual counting within three 5-m2 areas atmilk and soft dough stages. Mechanical tally counterswere used to record the number of leaves, tillers(including deadhearts and whiteheads), and insects asappropriate. One staff member served as a recorderduring sampling.

Rice plant- and leafhoppers and their key predatorswere sampled by sweep net and visual counting on aper-area basis in Pangasinan and Iloilo in insecticideuntreated fields. A standard 38-cm diameter sweep netwas used for the more mobile species with the operatormaking pendulum swings while walking through thefield. In each field, 20 sweeps were taken in thevegetative, reproductive, and ripening growth stages.The contents were placed in large plastic bags andchloroform-soaked cotton balls were added to kill theinsects which were then identified and counted. For themore sedentary species, 1 m2 was marked off and alltillers within the sampling area were inspected forhomopterans, herbivores, and predators which werecounted by a team of three people, two doing thecounting and one doing the recording. This was doneonce in the three major growth stages in five samplingsof 1 m2 per sampling date per field.

Insect parasitism rates were also measured byweekly visits to farmers’ fields untreated by insecticide.The various stages of common insect pests werecollected live and brought to the field office and heldin vials, fabricated plastic cages, or Petri dishes forparasitoid emergence (Barrion and Litsinger 1985).Plant-/leafhopper eggs were detected from tiller dissec-tion and held on moist seed germination cards in Petridishes with an added fungistatic agent. Larvae held inrearing containers were checked regularly and re-freshed with new leaves. Stemborer larvae, detectedfrom stem dissection and damaged tillers, were rearedon tillers in long glass vials. Adult plant-/leafhopperswere inspected for Strepsiptera under a stereomicro-scope or held for dryinid or pipunculid parasitoidemergence in special plastic cages (Chandra 1978).

2.6. Light trap collections

Kerosene light traps (Litsinger and EntomologyDepartment 1979) were operated daily to census riceinsect pests in one village per each of the three sites. Afarmer was trained to manage each light trap bycollecting and placing nightly catches in vials of 70%alcohol while trained staff identified and counted.Light traps were placed in pairs per village in open ricefields at least 100 m apart. Enough kerosene was usedso that the lamps burned all night. The height of theflame was standardised by wick length. Collections inthe three RWR sites were compared to four establishedin dryland rice sites (Siniloan, Quezon; Claveria,Misamis Oriental; Tupi, South Cotabato; Tanauan,Batangas) (Litsinger et al. 2009) and three irrigatedsites (Koronadal, S. Cotabato; Victoria/Santa Maria,Laguna; Zaragoza/Cabanatuan/Jaen, Nueva Ecija)(Litsinger et al. 2005) where similar research teamsworked and paired light traps were managed byfarmers. Two irrigated sites were subdivided intosynchronously and asynchronously planted double-cropped rice areas in Koronadal and Jaen (Loevinsohnet al. 1988). Counts of all light trap collections weresummed over a 6-month period to represent theduration of each seasonal rice crop. This was done sothat RWR single crop sites could be compared toirrigated double crop sites on an equal per-crop basis.In irrigated sites, data for each species were sum-marised for each wet and dry season crop based on theplanting pattern each year.

2.7. Ecosystem comparisons

RWR arthropod fauna and yield losses in the threeRWR sites were compared to the irrigated and drylandrice sites which also employed the same arthropodsampling and partitioned-growth-stage insecticidecheck methods. On-farm insect pest sampling andyield loss trials were conducted in the same threeirrigated, double-crop and four dryland rice areasmentioned above.

Farm record keeping was conducted in each of thesites during the crops where light traps were operating.Accordingly 20–40 farmers were interviewed in eachsite by the local staff to determine applied kg N/ha andnumber of insecticide applications per crop. Mathe-matical models of best fit correlating each of the twoinput levels to seasonal light trap totals for selectedinsect pests over a range of sites in each of the threeagro-ecosystems were analysed by regression analysis.

2.8. Statistical analysis

All statistical analyses were performed by SAS withP � 0.05 as the criterion for significance. Results weresubjected to one-way ANOVA and regression analyseswhere appropriate. Treatment means were separated


using the paired t-test for two variables or LeastSignificant Difference (LSD) test for more than twovariables. Means are shown with standard errors of themean (SEM) using a pooled estimate of error variance.

3. Results

3.1. Insect pest and natural enemy fauna

Rice whorl maggot was prevalent in all RWRlocations. The ephydrid fly’s larva tunnels into newlydeveloping leaves producing a characteristic feedinginjury along the edges when they unfold (Ferino 1968).Loss results from reduced photosynthetic area anddisruption of vascular flow. Percent damaged leaveswas highest on all crops in Pangasinan among sites andincluding traditional (29%) and modern cultivars onthe single crop (36%), as well as first (23%) and second(25%) crops of the double crop pattern (Table 2). Onlyin Cagayan was incidence significantly higher ontraditional (21%) than modern (5%) varieties. Lowestincidence (6–7% damaged leaves) was in Iloilo in boththe first and second crops.

Rice caseworm, the most prevalent lepidopterandefoliator in the RWR sites, is a semi-aquatic pyralidwhose larva cuts off the tips of young rice leaves thatfall onto the water surface before naturally rolling intotubes in which it seeks shelter (Litsinger et al. 1994a).Most feeding occurs at night, but during the day thefloating larvae in their cases are swept toward theleeward side of fields by wind or by water coursing tolower-lying fields in the watershed. The greatestconcentration of damage occurs after rains flush‘upstream’ larvae to bottomland fields, particularlyduring the vegetative stage. In the sloping topographyof Iloilo, rice fields drain from a larger watershed thanoccurs in other sites resulting in a greater concentrationeffect where a high of 29% damaged leaves wasrecorded in the first crop of the double crop pattern(Table 2). Moderate damage levels (17–18%) occurredin traditional varieties in Iloilo and Pangasinan withleast (4%) in the single crop in Cagayan with modernvarieties.

The green hairy caterpillar was more encounteredthan the green semilooper (both noctuids) in the threeRWR sites, but both vegetative stage defoliatorsoccurred at very low levels. Other common defoliatorswere the satyrid greenhorned caterpillar Melanitis ledaismene (Cramer) and the hesperiid rice skipperPelopidas mathias (F.). The former blends into thebright green foliage, thus even though large, the larvaeare often overlooked (Litsinger et al. 1993). Thehesperiid also is less noticed as its larvae live withintightly folded leaves (Litsinger et al. 1994b). Both ofthese species are most often encountered in thereproductive rice stage. A wide range of grasshopperscan be found in RWR, but like the butterflies are low indensity. A range of noctuid armyworms and cutwormscan attack the vegetative stage, at times in large

numbers particularly after a drought (Mochida et al.1987). The panicle-cutting caterpillar Mythimna separ-ata (Walker) can cause significant loss as it oftenaggregates, while Spodoptera litura F. cutworm wasobserved in Cagayan after building up on weeds thenshifting to rice after the farmer hand weeded. Defolia-tion levels from all of these species, save caseworm,were insignificant in the trial fields. Despite its commonname M. separata rarely was noticed affecting panicles.

The highest stemborer damage occurred in tradi-tional varieties in Iloilo and Pangasinan averaging 11–16% deadhearts and 9–11% whiteheads (Table 2). Thenext highest level occurred in the single crop inPangasinan on modern rices with 11% deadhearts,but 52% whiteheads. Least damage occurred in thesingle transplanted crop in Cagayan on modern rices(51%) followed by the first wet seeded crop inPangasinan (54%). Tiller dissections showed thatScirpophaga stemborers predominated in all three siteswith Pangasinan registering only yellow stemborer S.incertulas (Walker) (Table 3). The principal species inIloilo was white stemborer S. innotata (Walker) whichalong with yellow borer totalled five species includingstriped stemborer Chilo suppressalis (Walker), pinkstemborer Sesamia inferens (Walker), and gold fringedstemborer Chilo auricilius Dudgeon, while Cagayanhad four.

Three leaffolder species were encountered in theRWR sites with Marasmia exigua (Butler) being moreprevalent than Cnaphalocrocis medinalis (Guenee), asthe former has a wider host plant range (Barrion et al.1991). M. patnalis Bradley was also noted. The greatestabundance was recorded on the traditional varieties ofIloilo (10% damaged flag leaves) and the first ricecrops in both Pangasinan (9%) and Iloilo (7%)(Table 2). The lowest defoliation was recorded in thesecond crops of Iloilo and Pangasinan (1–3%). Riceseed bug was dominated by Leptocorisa oratorius (F.),with L. acuta (Thunberg) being rarely found. Highestincidence (bugs per m2) was in the second crop of Iloilo(7 bugs), followed by traditional rice in Iloilo and thesingle transplanted crop in Cagayan (4–5 bugs)(Table 2). Least incidence (52 bugs) occurred in thefirst and single crops of Pangasinan and the first cropin Iloilo. Farmers do not receive a price deduction forpecky rice thus the rice seed bug is less of a pest than inother countries that value grain quality.

The Iloilo and Pangasinan sites were sampled forrice hoppers and their key predators both on tradi-tional and modern rices (Table 4). Nephotettixnigropictus (Stal) was the most dominant greenleafhopper on both traditional and modern varietiesin both sites. Six-fold more N. nigropictus werecensused from traditional varieties than on modernones in Iloilo, while in Pangasinan the ratio was 3-fold.The modern rices IR28 and IR36 had resistance toboth Nephotettix species. A disease flare-up of tungrooccurred in Iloilo on traditional varieties in 1976 but


Table

2.

Insect

pestdensities

from

single

anddouble

croprainfedwetlandrice

from

threesitescomparinghighyieldingmodernvarietialtypes

totraditionalrices.

Resultsfrom

rainfedrice

are

comparedto

fourdrylandandfourirrigatedrice

sites.Philippines,1976–91.1

Culture

Site

Province

Years

Planting

method2

No.

crops

Variety

No.

fields

Whorlmaggot

(%DL)21–35

DT/D

AS

Defoliators

(%DL)21–35

DT/D

AS

Stemborerdamage(%

)Leaffolders

(%damaged

flagleaves)

Riceseed

bug(no./m

2)

milkstage

Deadhearts

Whiteheads

Rainfedwetland

Single

crop-traditionalvarieties

Oton/Tigbauan

Iloilo

1976–78

TP

3BE3,Kapoypoy

13

7.9+

4.8

c16.5+

11.4

ab4

15.9+

6.8

a9.0+

4.5

a9.5+

4.8

ab

3.8+

2.0

ab

Solana

Cagayan

1980–82

TP

3Wagwag

13

21.3+

8.3

b11.0+

9.2

bc4

0.6+

0.3

c1.4+

0.7

c3.7+

3.8

bc

2.2+

1.1

bc

Manaoag

Pangasinan

1976,79–80

TP

3Wagwag,Inano

15

28.7+

4.1

ab

17.9+

2.8

ab4

11.2+

6.7

ab

11.1+

5.8

a4.4+

1.3

bc

2.6+

1.8

bc

Single

crop-modernvarieties

Solana

Cagayan

1980–82

TP

3IR

36,52

16

5.1+

3.2

c3.7+

2.5

c40.7+

0.4

c0.6+

0.2

c3.0+

0.9

bc

5.2+

2.4

ab

Manaoag

Pangasinan

1976–80

TP

6IR

28,36

33

35.8+

13.5

a11.7+

6.9

bc4

10.8+

5.6

ab

1.6+

1.0

c4.8+

3.5

bc

1.4+

0.9

cDouble

crop-firstcropmodernvarieties

Manaoag

Pangasinan

1976,79–80

WS

3IR

28,36

12

23.3+

19.1

ab

7.8+

4.4

bc4

3.1+

2.2

c1.3+

1.1

c8.9+

10.5

ab

1.9+

1.6

cOton/Tigbauan

Iloilo

1976–79

WS

4IR

28,36

21

5.9+

1.1

c29.4+

27.3

a4

1.6+

1.3

c3.5+

1.6

bc

7.2+

5.6

ab

2.1+

1.7

cDouble

crop-secondcropmodernvarieties

Manaoag

Pangasinan

1976–80

TP

6IR

28,36

30

24.6+

18.2

ab

6.2+

3.6

bc4

8.3+

4.1

b2.7+

1.7

c3.3+

1.7

c2.5+

1.4

bc

Oton/Tigbauan

Iloilo

1976–79

TP

4IR

28,36

19

6.7+

9.0

c8.4+

8.7

bc4

9.9+

4.1

b4.4+

2.3

bc

1.4+

1.1

c6.8+

4.3

aRainfeddryland

Single


Siniloan

Quezon

1984–85

DS

2Benernal

803

03

0.0

c0c

0c

4.9+

2.7

ab

Tanauan

Batangas

1976–80

DS

5Dagge

25

03

03

1.6+

0.5

c2.6+

0.8

c17.3+

5.1

a1.3+

1.6

cSingle


Claveria

MisamisOriental

1984–90

DS

7UPLRi5

37

03

03

0.6+

0.3

c0.5+

0.2

c1.2+

0.3

c1.0+

2.1

cTupi

S.Cotabato

1988–90

DS

3UPLRi5

19

03

03

0.5+

0.3

c0.7+

0.3

c6.5+

2.8

bc

1.0+

0.9

cTanauan

Batangas

1978–80

DS

3UPLRi5

13

03

03

0.5+

0.2

c1.5+

0.6

c9.6+

4.0

ab

1.3+

0.9

cIrrigatedwetland

Double

crop-wet

seasonmodernvarieties

Zaragoza

NuevaEcija

1979–91

TP

12

IR36,42,52,56

72

20.4+

2.2

bc

11.0+

2.4

bc5

1.7+

0.4

c2.7+

0.7

c6.2+

1.2

bc

0.2+

0.3

cGuim

ba

NuevaEcija

1984–91

TP

7IR

58,64

44

7.4+

2.9

c7.5+

2.8

bc5

1.7+

0.5

c4.7+

1.0

bc

2.3+

1.4

c1.3+

3.1

cKoronadal

S.Cotabato

1983–91

TP

7IR

60

52

25.0+

2.9

ab

9.7+

2.8

bc5

1.5+

0.5

c2.5+

1.0

c3.5+

1.4

c1.0+

0.2

cCalauan

Laguna

1984–91

TP

9C1

44

11.4+

3.1

c0.9+

3.0

c51.6+

0.5

c2.3+

0.9

c1.0+

1.3

c0.6+

0.6

cDouble

crop-dry

seasonmodernvarieties

Zaragoza

NuevaEcija

1979–91

TP

11

IR36,42,52,56

69

19.2+

2.6

bc

3.6+

2.6

c51.1+

0.5

c2.0+

0.8

c4.2+

1.2

bc

0.1+

0.1

cGuim

ba

NuevaEcija

1984–91

TP

6IR

58,64

44

11.5+

3.1

c1.5+

3.0

c54.7+

1.0

bc

2.4+

1.1

c1.0+

1.5

c0.2+

0.1

cKoronadal

S.Cotabato

1983–91

TP

8IR

60

57

19.5+

2.7

bc

6.0+

2.6

bc5

1.8+

0.5

c2.4+

0.9

c7.5+

1.3

ab

0.9+

0.6

cCalauan

Laguna

1984–91

TP

8C1

37

5.8+

2.7

c0.8+

2.8

c52.9+

0.5

c1.6+

0.9

c0.4+

1.3

c1.3+

0.7

cP

50.0001

50.003

50.0001

0.0006

50.0001

50.0001

F9.15

2.62

6.81

2.73

3.52

3.64

df

93

86

113

116

114

105

1DL¼

damaged

leaves,DT¼

daysafter

transplanting,DAS¼

daysafter

sowing.

Inacolumn,meansseparatedbydifferentlettersare

significantlydifferent(P�

0.05)byLSD

test,data

averaged

per

crop.

2TP¼

transplanted,DS¼

directseeded

indry

soil,WS¼

wet

seeded,directsownonpuddledsoil.

3Notobserved

intheenvironment.

4Mainly

caseworm

with51%

Rivulaþ

Naranga.

5Mainly

Rivulaþ

Narangawith51%

caseworm

.


not in modern rices. The white leafhopper Cofanaspectra (Distant) achieved higher densities on tradi-tional cultivars in Iloilo, while in Pangasinan there wasno difference. On the other hand, the zigzag leafhopperRecilia dorsalis (Motschulsky), another vector oftungro, showed no difference in numbers by varietaltype or location.

High densities of brown planthopper occurred inIloilo on both traditional and modern rices but threetimes more on the former which are highly susceptible(Table 4). Whitebacked planthopper Sogatella furcifera(Horvath) occurred in greatest numbers in Iloilo onmodern rices. Isolated patches of hopperburn fromplanthoppers only occurred in Iloilo in 1977 on IR28and IR30. Despite the high incidence of greenleafhoppers and brown planthoppers in the RWRsites, the mirid predator Cyrtorhinus lividipennis Reutershowed no response in density either by site or cultivar.Spiders and ladybeetles, however, were more numerouson traditional rices in Iloilo where leafhopper andplanthopper numbers were higher as well as on modernrices in Iloilo attacked by brown planthopper. ThripsStenchaetothrips biformis (Bagnall) and mealybugsPseudococcus saccharicola Takahashi were noted onlyduring drought spells in all three sites.

Across the sites, lowest egg parasitism ratesoccurred on whorl maggot (0%) and caseworm(0.3%) (Table 5). Whorl maggot eggs have a calcareouschorion that no doubt retards parasitoid ovipositors,while caseworm eggs are laid underwater makinglocating them difficult (Litsinger et al. 1994a). InPangasinan, where whorl maggot was highly prevalent,larval parasitism averaged 19%, with only 1% in theother two sites. The semi-aquatic caseworm larvae alsoare rarely parasitised as shown by one larva in a sampleof 119 parasitised in Pangasinan. Other early-seasondefoliating Lepidoptera such as the green hairycaterpillar and cutworms registered low levels ofparasitism across the three sites. In Cagayan, whereS. litura was most abundant, larval parasitism reacheda high of 8%, but only 2% in Iloilo. M. separata larvalparasitism attained only 2–5% in the three sites.

Parasitism rates were higher on mid- and late-seasondefoliating Lepidoptera. Greenhorned caterpillar eggparasitism reached 15% in both Iloilo and Pangasinanbut was nil in Cagayan. Greenhorned larval parasitismaveraged 22% in Pangasinan but only 7–8% elsewhere.Rice skipper egg parasitism was nil in both Iloilo andCagayan. Larval parasitism was highest in Iloilo 26%with only 7–8% in the other two sites. Leaffolder eggsare very small thus were too difficult to assess, whilelarval parasitism was very low, averaging 2–5%.

Turning to stemborers, some of the highest para-sitism rates occurred in Pangasinan with Scirpophagaeggs 33% but only 6–8% in the other sites. Scirpophagalarval parasitism was also high in Pangasinan 32% but2–6% elsewhere. Larval parasitism for the otherstemborer species ranged from 0 to 7%, the highestbeing of pink stemborer in Cagayan. Leafhopper eggparasitism was high in all three sites ranging from 17 to35%. The white leafhopper C. spectra revealed 17%egg parasitism, while surprisingly zigzag leafhopper R.dorsalis registered only 0–1%. Leafhopper nymphs andadults are parasitised mainly by pipunculid flies whichreached 4–7% on Nephotettix spp. and 0–1% onzigzag. Results were similar for planthoppers. Eggparasitism of N. lugens registered 14–31% while S.furcifera showed similar numbers 18–29%. Nymphsand adults are parasitised mainly by Strepsiptera anddryinids where together on N. lugens they attained ahigh of 12% in Pangasinan but 2–4% elsewhere. S.furcifera produced somewhat lower numbers: 7% inPangasinan and 0–2% elsewhere.

3.2. Yield losses

Traditional tall varieties in Cagayan and Pangasinanyielded just under 2 t/ha in the unprotected plots butregistered a mean 19% yield loss (range 13–25%) or 0.4t/ha (range 0.1–0.7 t/ha) (Table 6). But only the meanloss in the higher yielding Pangasinan site wassignificant (P ¼ 0.02, F ¼ 6.70, df ¼ 15), with greatestloss (16%) in the vegetative stage. In Cagayan in thesame single-cropped, transplanted culture, yields and

Table 3. Stemborer species prevalence determined from tiller dissections at the reproductive stage in three rainfed wetland sites,Philippines, 1976–82.

Tiller dissections1

Relative abundance (%)

Site Province Years VarietyCrops(no.)

Scirpophagaspp.2

Chilosuppressalis

Sesamiainferens

Chiloauricilius n

Oton/Tigbauan Iloilo 1976–78 IR36 3 60.1 24.1 8.3 7.5 150 hillsManaoag Pangasinan 1977–79 IR36 4 100 0 0 0 200 hillsSolana Cagayan 1980–82 IR36, IR52 3 77.0 4.1 13.3 5.6 150 hills

1One field was sampled per crop that had not been treated with insecticide. Sample size was 50 hills/field. In each site the percentages add to100%.2White and yellow stemborers are indistingishable in the larval stage thus they are not separated by species. White stemborer does not occur inLuzon thus in Pangasinan and Cagayan all Scirpophaga specimens were yellow, while in Iloilo there was a mixture.


losses with modern varieties were similar to those oftraditional rices. Mean losses were higher on modern(22%) than traditional (13%) rices, but not signifi-cantly due to the high yield variability in this risk pronesite. However, yield potential of modern varietiesincreased substantially in Pangasinan in the singlecrop from 1.9 to 3.6 t/ha in untreated plots in a lessrisky environment. In Pangasinan the percentage yieldlosses (also significant P ¼ 0.0004, F ¼ 14.07. df ¼ 55)were similar for both traditional and modern rices (24–25%), but tonnage loss was higher in the latter (0.7 vs.1.1 t/ha) with the greatest loss occurring in thevegetative stage (11%).

In the first wet-seeded crop of the double-crop inboth Pangasinan and Iloilo, losses were insignificant,averaging only 2 and 16%, respectively. Losses in Iloilowere higher in years where planting was delayed beyondMay as earlier plantings tended to escape pest attack.First crop plantings in Pangasinan were more timelythan in Iloilo over years. Highest crop stage losses inIloilo again were in the vegetative stage (8%). Inthe second transplanted crop, untreated yields wereover 1 t/ha lower than in the first crop in both sites,underscoring the higher risk of late season drought inthe double crop system. Losses in the second crop werehigher than in the first (18–28 vs. 2–16%) in both sites.Significant losses were 0.7 t/ha in Pangasinan (P ¼ 0.01,F ¼ 7.83, df ¼ 44) and 1 t/ha in Iloilo (P ¼ 0.02,F ¼ 6.87, df ¼ 35) where the untreated averaged 2.6–3.0 t/ha. Losses were higher in the single vs. the secondcrop in Pangasinan (24 vs. 18%) even though yield inthe unprotected plots was higher in the former (3.6 vs.3.0 t/ha) showing the greatest stress was in the secondcrop. Once more losses were highest (13%) in thevegetative stage of the second crop.

3.3. Chemical control

Prophylactic insecticide application led to significantyield increases in the single rice crop with bothtraditional and modern rices in Pangasinan and inIloilo in both the first and second crops with modernrices (Table 7). Almost half of the fields (47%)exceeded an action threshold over the three sites andfour categories of crops, with most of the applicationsdirected at the vegetative stage against whorl maggot.However, significant yield increases in the three-application, prophylactic regime occurred in four ofthe seven crop cultures 6 sites 6 varieties tested. InPangasinan and Iloilo, yield gains were higher (0.5–0.6 t/ha) in the prophylactic treatment than for actionthresholds (0.2–0.3 t/ha). In Pangasinan significantgains occurred in single-crop rice for both traditionaland modern rices. Between 38 and 50% of traditionalrice fields surpassed action thresholds for whorlmaggot and armyworm in Pangasinan and Cagayan,respectively, but only in Pangasinan was there asignificant yield response of 0.2 t/ha.T

able

4.

Comparisonofrice

hoppersandtheirpredators

intw

orainfedwetlandsitesforboth

traditionalandmodernvarietiesusingtw

osamplingmethods:1)net

sweepsforfast

movinginsectsthatinhabitthetopofthecanopyand2)per

areaformore

sedentary

specieslyingbelow,OtonandTigbauan,IloiloandManaoag,Pangasinan,1976–79.1

Site

No.

crops

No.

fields

Per

10net

sweeps2

(Per

m2)3

N.virescens

N.nigropictus

C.spectra

R.dorsalis

S.furcifera

Coccinellids

N.lugens

Cyrtorhinus

Spiders

Traditionalvarieties4

Iloilo

311

13.2+

8.6

a81.3+

54.9

a16.7+

7.0

a7.7+

6.7

a7.7+

5.9

b17.9+

6.9

a149.3+

148.0

a3.3+

2.9

a53.7+

19.0

aPangasinan

311

20.3+

17.2

a60.8+

21.7

a1.7+

1.2

b2.0+

1.0

a4.0+

2.6

b2.8+

1.9

b8.7+

8.1

b3.3+

5.8

a12.0+

8.5

cModernvarieties5

Iloilo

526

1.8+

5.2

b6.7+

4.2

b6.3+

8.6

ab

1.8+

1.3

a23.2+

22.7

a7.4+

8.4

ab

48.6+

41.7

a3.6+

4.2

a30.6+

17.2

bPangasinan

635

1.4+

5.1

b5.6+

7.8

b3.4+

5.4

b1.2+

0.4

a3.0+

2.1

b1.9+

2.1

b9.2+

7.2

b12.6+

21.0

a11.6+

7.8

cP

50.0001

50.0001

0.03

ns

0.04

0.03

0.02

ns

0.01

F7.65

8.55

4.37

1.21

4.88

4.01

4.32

2.06

6.54

df

16

16

16

16

16

16

16

16

16

1In

acolumn,meansseparatedbydifferentlettersare

significantlydifferent(P�

0.05)byLSD

test,data

averaged

per

crop.

220net

sweepsper

crop,sampledthreetimes

per

cropatvegetative,

reproductive,

andripeningstages.

3Threesamplesper

croponce

each

inthevegetative,

reproductive,

andripeningstages,fivesamplesof1m

2weretaken

each

date.

4BE3andKapopoyin

Iloilo,WagwagandInanoin

Pangasinan.

5IR

28,IR

36.


Table5.

Parasitism

ofthecommoninsect

pestsofirrigateddoublecropped

rice

sitesin

tropicalAsiaasreported

intheliterature

comparedto

single-crop,rainfed,wetlandrice

sites

inthreeprovinces,Philippines,1976–83.

Parasitism

(%)1

Rainfedwetlandecosystem

Iloilo2

Pangasinan3

Cagayan4

Irrigatedwetlandecosystem

Pest

Stage

%n

%n

%n

Allsites(m

ean%

)%

nno.crops

Citation

Hydrellia

philippina

Egg

0132

0243

053

00

4500

3vanden

Berget

al.1988

Larva

1.1

89

19.4

119

0.9

71

7.1

35.0

475

3Ferino1968

Nymphula

depunctalis

Larva

043

0.8

119

035

0.3

Rivula

atimeta

Larva

0369

3.9

109

1.2

56

1.7

Mythim

naseparata

Larva

5.4

175

1.8

111

2.9

57

3.4

Spodoptera

litura

Larva

2.3

97

7.9

126

5.1

Melanitisledaismene

Egg

14.7

119

14.9

40

086

9.9

20.8

844

410

Litsinger

etal.1997

Larva

7.5

301

22.4

857

6.9

163

12.3

10.1

2361

410

Litsinger

etal.1997

Pelopidasmathias

Egg

021

021

0.0

14.2

762

410

Litsinger

etal.1997

Larva

26.0

37

10.4

146

7.8

118

14.7

13.5

2077

410

Litsinger

etal.1997

Cnaphalocrocismedinalis,

Larva

1.7

418

5.1

39

2.4

67

3.1

40

4904

2Arida&

Shepard

1990

Marasm

iaspp.

35.9

41000

6deKraker

etal.1999

Scirpophagaspp.

Egg

5.9

201

32.5

130

8.4

78

15.6

50

41000

2Shepard

&Arida1986

30.3

41000

3Rothschild1970

59.5

54

1000

1Litsinger

etal.2006c

Larva

1.5

401

31.8

133

4.5

87

12.6

0.4–3

147

3Rothschild1970

Chilospp.

Larva

1.8

33

3.2

55

2.5

12

29

3Rothschild1970

Sesamia

inferens

Larva

034

7.1

39

3.6

19

50

3Rothschild1970

Nephotettix

spp.

Egg

16.5

1253

34.6

480

30.4

454

27.2

22.0

41000

1IR

RI1978

Adult

3.6

850

7.0

1,411

6.0

567

5.5

20.5

41000

2IR

RI1978,1979

21.5

41000

2Pena&

Shepard

1986

Recilia

dorsalis

Egg

0186

1.2

345

18.5

Adult

0200

0.9

334

0.5

Cofanaspectra

Egg

17.0

37

17.0

8.0

41000

1IR

RI1983

Nilaparvata

lugens

Egg

19.7

876

13.8

520

31.3

628

21.6

26.3

41000

3IR

RI1978,1980b

Adult

1.8

850

12.0

395

4.3

546

6.0

8.5

41000

2IR

RI1978,1979

12

41000

2Pena&

Shepard

1986

Sogatellafurcifera

Egg

18.1

539

28.7

332

27.4

340

24.7

25

41000

2IR

RI1978,1981b

Adult

0.4

79

6.5

390

2.3

156

3.1

8.3

41000

3IR

RI1978,1979,1981b

18

41000

2Pena&

Shepard

1986

1Eggs/eggmasses

andlarvaecollectedfrom

thefieldonexcisedleaves

wereheldin

vialsandpetridishes

forparasitoid

emergence.

2Meanofthreecrops1976–78.

3Meanoftw

ocrops1976–77.

4Meanofthreecrops1981–83.

5Synchronousplantedareaonly.


Table6.

Yield

loss

calculatedbythepartitioned

growth

stageinsecticidecheckmethodforthreesingleanddoublecropped

rainfedwetlandrice

sitesinvolvingtraditionalandhigh

yieldingmodernvarieties.Further

comparisonwasmadewithfourdrylandandfourirrigateddouble

cropped

sites,Philippines

1976–91.

Yield

loss

Yield

(t/ha)

Total

Bygrowth

stage(%

)

Cropagro-ecosystem

Site

Province

Crops

Protected

Untreated

t/ha1

%Vegetative

Reproductive

Ripening

Rainfedwetland

Single

croptransplanted-traditionalvarieties

Solana

Cagayan

31.84

1.73

0.11ns

13

65

2Manaoag

Pangasinan

22.58

1.94

0.65*

25

16

54

Average

2.21

1.84

0.38

19

11

53

Single

croptransplanted-modernvarieties

Solana

Cagayan

31.99

1.65

0.34ns

22

88

6Manaoag

Pangasinan

54.72

3.61

1.12**

24

11

76

Average

3.36

2.63

0.73

23

10

86

First

cropwet

seeded

-modernvarieties

Oton/Tigbauan

Iloilo

44.52

3.84

0.68ns

16

84

4Manaoag

Pangasinan

34.10

4.00

0.10ns

20.1

1.3

70.2

Average

4.31

3.92

0.39

94

32

Secondcroptransplanted-modernvarieties

Oton/Tigbauan

Iloilo

43.65

2.56

1.09*

28

13

69

Manaoag

Pangasinan

53.70

3.02

0.68*

18

12

33

Average

3.68

2.79

0.89

23

13

56

Rainfeddryland

Traditionalvarieties

Siniloan

Quezon

20.48

0.06

0.42***

88

Tanauan

Batangas

52.90

2.85

0.05ns

2Average

1.69

1.46

0.24

45

Modernvarieties

Claveria

MisamisOriental

73.43

2.64

0.79*

23

14

72

Tupi

S.Cotabato

43.46

2.96

0.50ns

15

78

0Tanauan

Batangas

34.01

3.61

0.40ns

18

12

42

Average

3.63

3.07

0.56

19

11

61

Irrigatedwetland

Wet

seasontransplanted-modernvarieties

Zaragoza

NuevaEcija

12

5.09

4.42

0.70***

13

55

3Koronadal

S.Cotabato

75.16

4.55

0.60***

11

44

3Guim

ba

NuevaEcija

74.39

3.67

0.72***

22

97

5Calauan

Laguna

94.61

4.27

0.30***

64

11

Dry

seasontransplanted-modernvarieties

Zaragoza

NuevaEcija

11

6.23

5.50

0.63***

10

44

2Koronadal

S.Cotabato

84.85

4.10

0.75***

15

74

3Guim

ba

NuevaEcija

64.80

4.03

0.77***

18

58

5Calauan

Laguna

84.79

4.38

0.39***

82

42

Average

4.99

4.37

0.61

13

55

3

1Levelsofsignificance

betweenprotected

anduntreated:ns(P

40.05),*(P

50.05),**(P

50.01),***(P

50.0001).


Only 24% of fields in the single crop rice withmodern rices in Pangasinan exceeded thresholdswhich involved whorl maggot, Naranga/Rivula defo-liators, and leaffolders. In the double crop pattern,action thresholds were most frequently surpassed inIloilo, 86% in the first crop and 95% in the secondfrom whorl maggot, caseworm, stemborers, and riceseed bug. Fewer fields in Pangasinan (13 and 25%)exceeded the action thresholds in each crop of thedouble crop pattern which was more or less equal tothat in the single crop pattern. Leaffolders were theonly insect pests in the first crop, whereas whorlmaggot and rice seed bug occurred in the second cropin Pangasinan.

Economic analyses showed that in no case wasthere an acceptable profit from chemical control, as inonly one crop (the single crop with modern rices inPangasinan) was there not a loss, but only produced areturn of 5$3/ha. The prophylactic regime fared evenworse with losses per crop in the order of $38–50/ha.Therefore the benefit: cost ratios in all cases areunacceptable to farmers.

3.4. Ecosystem comparisons

RWR arthropod populations were compared to sites indryland and irrigated environments based on light trapcollections, rice field sampling, and yield lossassessments.

3.4.1. Light trap collections

Light trap seasonal totals of daily collections give anindication of relative abundance within a radius of 0.5–1 km, the mean dispersal distance of most commonrice insects (Loevinsohn et al. 1988). Light traps wereless attractive to leaffolders, caseworm, and otherlepidopterous defoliators thus they were not included.First, averaging the crop totals over each agroecosys-tem and planting synchrony type (see the riceagroecosystem classification averages in the bottomhalf of Table 8), brown and whitebacked planthoppers,zigzag leafhopper, and the Cyrtorhinus predatorregistered highest collections in the asynchronousirrigated agroecosystem, while there were no differ-ences among RWR, dryland, and synchronous irri-gated agroecosystems. Notably, the RWRagroecosystem was statistically equal to the asynchro-nous, irrigated system with regard to the abundance ofgreen leafhoppers, and more than the two otheragroecosystems. With regard to Scirpophaga stem-borers, densities were higher in the asynchronousirrigated agroecosystem than in the dryland sites,with RWR and synchronous irrigated systems beingintermediate. There were no differences among agroe-cosystems regarding white leafhopper and non-Scirpo-phaga stemborers. The two asynchronous multi-ricecropped sites were: (1) Zaragoza which was at theT

able

7.

Perform

ance

intheuse

ofactionthresholdsforinsecticidedecisionmakingin

threerainfedwetlandrice

sitescomparedto

use

ofaprophylactic

application,Philippines,

1976–82.

Culture

Site

Province

Planting

method1

Variety

Yield

(t/ha)2

%fields

treated

foraction

threshold

Target

pests3

Yield

difference

from

untreated(t/ha)4

Return

($/ha)5

Full

protection

Untreated

Action

threshold

Significance

Prophylactic

Significance

Action

threshold

Prophylactic

Single


Solana

Cagayan

TP

Wagwag

1.27

0.82

38

WM,AW

0.17

ns

0.22

ns

Manaoag

Pangasinan

TP

Wagwag

2.22

1.73

50

WM

0.23

*0.50

**

79.08

746.70

Single


Manaoag

Pangasinan

TP

IR28,36

4.93

4.02

24

WM,DEF,LF

0.32

*0.56

**

2.40

740.01

Double

crop-firstcropmodernvarieties

Manaoag

Pangasinan

WS

IR28,36

3.76

3.71

25

LF

70.01

ns

0.02

ns

Oton/Tigbauan

Iloilo

WS

IR28,36

4.56

3.92

86

WM,CW,RB

0.29

ns

0.58

**

737.45

Double

crop-secondcropmodernvarieties

Manaoag

Pangasinan

TP

IR28,36

2.77

2.45

13

WM,RB

0.16

ns

0.30

ns

Oton/Tigbauan

Iloilo

TP

IR28,36

3.76

2.56

95

SB,RB

0.27

ns

0.48

*7

50.25

Average

47.3

1TP¼

transplanted,WS¼

pre-germinateddirectwet

seeded

rice.

2Thefullprotectiontreatm

entshowstheyield

potentialfrom

insecticideapplicationwhiletheuntreatedactsasacontrol.

3WM¼

whorlmaggot.AW¼

arm

yworm

,DEF¼

Naranga/R

ivula

defoliators,LF¼

leaffolders,CW¼

caseworm

,RB¼

rice

seed

bug,SB¼

stem

borers.

4Levelsofsignificance:ns(P

40.05),*(P

50.05),**(P

50.01).

5Aneconomic

analysiswasperform

edonly

onthose

cropsandtreatm

ents

wheretherewasasignificantincrease

inyield.


Table8.

Abundance

ofinsectsandfactors

inrice

croppingintensity

byrice

agroecosystem

asdetermined

from

kerosenelighttrapssetupin

twelvesitesin

thePhilippines,1979–91.

Rice

ecosystem

1Town

Province

No.

crops/

year

Areain

rice

(%)2

kgN/

ha3

No.

insect-cide

applications/

crop3

No.

crops

Seasonaltotalper

lighttrapper

location4

Brown

planthopper

N.lugens

Whitebacked

planthopper

S.furcifera

Green

leafhoppers

Nephotettix

spp.

Zigzag

leafhopper

R.dorsalis

White

leafhopper

C.spectra

C.lividipennis

mirid

predator

Scirpophaga

spp.stem

borers

5Other

stem

borers

6

Siteaverages

Dryland

Siniloan

Laguna/

Quezon

1.0

35

02

185+

78d

451+

144c

425+

158b

41+

7c

Claveria

Misamis

Oriental

1.0

940

02

262+

75d

130+

37b

75+

29c

190+

73c

37+

19b

45+

11c

178+

98c

Tupi

South

Cotabato

1.0

14

30

03

2,908+

864c

498+

115b

1,449+

398c

1,802+

161b

80+

22b

1,780+

272b

170+

43c

315+

87bc

Tanauan

Batangas

1.0

20

60

02

130+

78d

1,700+

367b

860+

452c

720+

294c

50+

23c

Rainfed

Solana

Cagayan

1.0

60

00.1

4491+

217d

1,527+

527b

3,218+

2,320b

312+

103ab

595+

269b

437+

133c

131+

36c

wetland

Manaoag

Pangasinan

1.0

85

20

0.4

2289+

94d

321+

81b

2,179+

538c

305+

79c

475+

66c

0c

Oton/

Tigbauan

Iloilo

1.0

85

30

1.3

21,824+

528cd

1,012+

215b

2,440+

770c

1,016+

612bc

458+

185a

455+

314b

997+

108b

38+

30c

Irrigated

(synchronous)

Victoria/

Sta

Maria

Laguna

1.9

90

40

3.0

3214+

79d

1,366+

896b

629+

426c

195+

95c

410+

168b

413+

88c

35+

35c

Cabanatuan/

Zaragoza

NuevaEcija

2.0

80

60

4.5

2154+

14d

361+

77c

305+

17c

0c

Koronadal

South

Cotabato

2.0

70

30

3.0

41,677+

345cd

549+

152b

2,279+

617c

855+

169c

93+

17b

706+

252b

662+

83bc

405+

46b

Irrigated

Jaen

NuevaEcija

2.0

80

60

4.5

215,224+

238a

9,207+

2,561a

137+

59c

0c

(asynchronous)

Koronadal

South

Cotabato

2.4

70

30

3.0

411,168+

1,849b

4,043+

1,117a

3,158+

501b

2,961+

389a

145+

21ab

7,169+

720a

2,519+

430a

751+

123a

P50.0001

50.0001

50.0001

50.0001

0.04

50.0001

50.0001

50.0001

F37.01

6.76

5.54

24.02

3.12

17.46

19.91

17.92

df

49

40

49

40

32

36

49

45

Riceagroecosystem

classificationaverage

Dryland

871b

776b

709b

904b

59

1,103b

77b

247

Rainfedwetland

868b

953b

2,612ab

661b

385

525b

636ab

56

Irrigated

682b

957b

650b

551b

93

558b

460ab

147

(synchronous)

Irrigated

13,196

a4,043a

6,183a

2,961a

145

7,169a

1,328a

376

(asynchronous)

P50.0001

0.04

0.02

0.02

0.12ns

0.007

0.04

0.07ns

F40.95

6.15

6.30

12.09

7.33

37.03

3.04

0.76

df

11

811

75

611

9

1Synchronyrefers

tofarm

ers’plantingdatesandsynchronyisdefined

when

farm

ersplantwithin

aperiodofonemonth,theaveragegenerationalperiodofmost

insect

pests.

2Riceareawithin

thecircumference

of1km

2aroundeach

lighttrapsiting.

3Basedonform

alandinform

alfarm

ersurveysduringtheseasonsoflighttrapcollection.

4Dailycounts

from

kerosenelighttrapsofsimilardesign.Nodata

indicatesthattheinsect

inquestionwasnotmeasured.Means(+

SEM)in

columns,followed

byacommonletter

are

notsignificantly

different(P

50.05)byLSD

analysis.

5S.innotata,S.incertulas.

6Chilo,Sesamia,Maliarpha.


tail-end of a large irrigation system and (2) Koronadalwhich had communal irrigation systems fed year-roundby free-flowing, artesian wells. Even though in both ofthese sites many farmers planted resistant rices, geneticresistance had broken down, probably due to acombination of multiple rice cropping which extendedpest generations and high insecticide usage whichcaused resurgence (Gallagher et al. 1994). On the otherhand, non-Scirpophaga stemborers and white leafhop-per showed no differences between rice cultures.

Among the RWR sites (see top half of Table 8),Iloilo had higher populations of brown planthopper,zigzag and white leafhoppers, and Scirpophagastemborers, while Cagayan had higher green leafhop-per densities. The three RWR sites were equal forwhitebacked planthopper, Cyrtorhinus predator, andnon-Scirpophaga stemborers. The two RWR anddryland sites with highest brown planthopper countswere those nearest to irrigated areas having extensiveplantings of susceptible varieties (Iloilo and Tupi).Focusing on brown planthopper, Iloilo was grown toa combination of susceptible (IR28 and traditionalrices) and resistant (IR36) varieties over time.Pangasinan had a similar mixture of resistant andsusceptible cultivars but was not near to an irrigatedrice area. Cagayan, like dryland sites, was plantedmainly with susceptible varieties but was a single croppattern and not situated near to irrigated sites. Twoof the irrigated rice sites in Laguna province andCabanatuan/Zaragoza, Nueva Ecija were dominatedby resistant cultivars which resulted in low densities asgenetic resistance held.

Green leafhoppers seemed to be highly favoured bywetland sites where long-maturing, traditional varietiesdominated. Cagayan was essentially a pure traditionalvariety site, while Iloilo and Pangasinan were sown tomixtures of modern rices and traditional types. Dry-land environments were planted to susceptible, short-season, traditional, japonica varieties planted highlysynchronously thus allowed only 2–3 generationscompared to 5–6 in Cagayan. Cyrtorhinus, a miridpredator of both planthopper and leafhopper eggs andyoung nymphs, responded more to planthopper thanleafhopper densities across ecosystems.

The Central Luzon sites in Pangasinan and NuevaEcija were pure yellow stemborer sites, whereas Iloilohad a mixture of white and yellow stemborers.Scirpophaga stemborers were dominant in RWRecosystems, whereas in dryland sites non-Scirpophagastemborers dominated. Iloilo and Cagayan were nearto large maize areas which fostered other species,whereas Pangasinan had only small maize areas earlyin the wet season as it was less elevated.

Dryland rice sites, with the exception of Tupi, hadthe smallest arthropod catches, probably due to thesmall rice area and limited growing season, character-istic of this ecosystem (Loevinsohn et al. 1988).Planthopper, stemborer, and leaffolder abundance

has been shown to be significantly influenced bynitrogen level and subject to insecticide resurgence(Litsinger 1994). Regression analyses of nitrogen ratesand insecticide frequency shown in Table 8 were notsignificantly correlated with abundance by linear ornon-linear models. The reason could be that theprevious confirming studies had been conducted atthe field level, whereas in the current study light trapssampled populations at the landscape level.

3.4.2. Field sampling

Whorl maggot, caseworm, and Naranga/Rivula wereobserved only in both wetland ecosystems (Table 2).The highest incidence of whorl maggot in the RWRecosystem consistently occurred in all crops in Panga-sinan (23–36% damaged leaves) as well as only thetraditional rice in Cagayan (21%). In the irrigatedecosystem, high incidence (19–25% damaged leaves)occurred in Zaragoza and Koronadal in both wet anddry season crops. Caseworm density was much higherin RWR (9–11% damaged leaves for both varietaltypes) than in irrigated rice on modern varieties(50.5% damaged leaves). In Iloilo, caseworm damagewas consistently higher than whorl maggot damage inall crops. Naranga/Rivula were more abundant inirrigated (5% damaged leaves) than in RWR (51%damaged leaves) ecosystems. Caseworm damage wastwice as high on average in the RWR agroecosystemthan Naranga/Rivula damage was in the irrigatedecosystem.

The two sites with the highest stemborer damagewere in the RWR agroecosystem (Iloilo and Pangasi-nan) especially on traditional varieties. Looking amongcrops grown to modern rices, the Pangasinan singlecrop had the highest stemborer incidence of all sites.The next highest sites were Iloilo second crop andGuimba, an irrigated site. Three of the sites with loweststemborer damage were in the drylands which matchedthe levels observed in Cagayan. Leaffolder damage wasgreatest in Batangas, a dryland site, ranging from (10to 17% damaged leaves) but was also equally high inIloilo on traditional rice, the first crop both in Iloiloand Pangasinan, as well as in irrigated Koronadal inthe dry season. Rice seed bug abundance was highest inmore crops in the RWR environment but least in thefour irrigated sites and three of the four dryland sites(the exception was the slash and burn rainforest site inSiniloan).

Although there were sites and crops in the RWRagroecosystem that had low densities for some pestclassifications (which was also true of all agroecosys-tems), RWR registered the highest proportion amongthe 6 pest 6 8 crop 6 variety categories in Table 2with overall statistically highest pest densities in 26%of occasions (14 of 54 categories), than the 10% indryland (3 of 30) or 4% in irrigated (2 of 48)ecosystems.


3.4.3. Yield losses

Yield losses also were compared across agroecosys-tems. The least biased method of measuring lossesacross sites and agroecosystems is percentage ratherthan tonnage. There was no difference in lossesbetween wet (0.58 t/ha and 13%) and dry (0.64 t/haand 13%) season, irrigated rice thus the two seasonswere combined (Table 6). Across agroecosystems andvarietal types, the highest percentage yield losses frominsect pests were traditional varieties of dryland rice.However this classification, composed of two sites, washighly influenced by the slash and burn site Siniloanwith an ‘off-the-chart’ 88% yield loss. The other site,Batangas, registered only a 2% loss; therefore thedifference was more a site effect than an ecosystemeffect. The dominant cropping pattern in RWRecosystems is the single crop, and losses there rangedfrom 19% for traditional and 23% for modern riceswith fairly consistent agreement within each site. Thismatches the mean yield loss in dryland rice withmodern varietal types (23%) and is greater than thatfor irrigated rice (13%). However, some irrigated ricesites such as Guimba were similar with 18–22% loss forboth wet and dry seasons. Comparing the three mainagroecosystems for modern varieties, losses in terms oftonnage ranged from 0.56 to 0.73 t/ha based on singlecrop RWR, the highest loss. However the 0.73 t/hafigure was high because of Pangasinan at 1.12 t/ha, thehighest loss for any site 6 crop 6 variety category.

The dryland agroecosystem had the highest andlowest yield losses while irrigated rice had a range ofsites from very low losses (6–8%) up to a maximum of22%. All of the RWR sites equalled or exceeded themaximum losses in irrigated rice. Thus, both therainfed ecosystems had on average higher losses thanthe more stable irrigated ecosystem.

4. Discussion

4.1. Insect pest and natural enemy fauna

As irrigated rice replaced RWR in favourable environ-ments, it is not surprising that the insect pest fauna arehighly similar. Flooding in both wetland ecosystemskills off soil pests which inhabit the dryland riceagroecosystem and attracts species that are adapted torice in standing water. Ponding restricts soil pests torice bunds. Of the common insect pests in thePhilippines in the more studied irrigated rice ecosystem(Litsinger et al. 2005), only green semilooper was lessencountered in the three RWR study sites. It isunknown why this is so as it has a wide host range(Pantua and Litsinger 1984). In terms of differences inpest abundance between irrigated and RWR, theresults of Table 2 show that site rather than ecosystemdifferences are more important. As RWR is moreprone to drought, insects favoured by those conditionssuch as thrips and mealybugs were occasionally noted

in the three study sites. These pests flourish in rice in allrice agroecosystems when under drought stress (Mo-chida et al. 1987).

A set of 10 characteristics inherent in RWR thatdefines this ecosystem in terms of pest prevalence canbe enumerated based on this study as well as theliterature: (1) large rice bunds that create drylandhabitat for soil pests, (2) more diverse natural floralhabitats and cropping patterns that provide alternativehosts and refugia, (3) low insecticide usage that allowsmore pest species to survive, (4) low inorganic fertiliserusage that engenders low yield potential, (5) morefluctuating paddy water levels that reduce performanceof granular pesticides and inorganic fertilisers, (6) morepest susceptible traditional varieties present, (7) beingtall, traditional varieties elongate over longer periodsmaking them more vulnerable to stemborers, (8) long-maturing traditional varieties promote more pestgenerations, (9) due to land fragmentation, sowingand transplanting are normally staggered over manymonths fostering pest build-up, particularly if rains aredelayed, but (10) a long rice-free dry season restrictsgenerational build-up of both pests and naturalenemies to only the wet season. Irrigated rice isnormally earlier maturing so cultural practices ofharvesting and land preparation for the dry seasoncrop break up pest cycles to a greater degree than inRWR for pests which reside in the stubble. With ashorter fallow period, most natural enemies tend to bemore favoured in irrigated multi-crop rice. The contextin which these factors affect densities of RWR pestguilds is elaborated in the following discussion.

Flooding in both wetland ecosystems kills off soilpests which inhabit the dryland rice ecosystem andattracts species that are adapted to rice in standingwater. Ponding restricts soil pests to rice bunds. RWRfields often have large bunds, some 41.5 m, asfarmers seek to maximise rainwater storage allowingdryland rice soil pests such as ants, termites, molecrickets, and white grubs to become occasional pests(Heinrichs et al. 1986). Infestations tend to occur inhigh-lying portions of uneven fields particularly onlight soils.

In a normal wet season, transplanting the singleRWR crop is delayed after the first rains while farmerswait for their fields to become saturated, a necessarystep for puddling the soil. Farmers first sow seedbeds,but as transplanting labour is normally scarce, farmfamilies can take many weeks to establish theirfragmented fields resulting in staggered plantings.Mechanisation which speeds up these operations inirrigated rice is not economical for a single rice crop,rainfed or irrigated. But if heavy rains arrive early,farmers can direct sow pre-germinated rice. Bothvolunteer rice and weeds emerge with the first heavyrains to provide habitat for rice arthropod develop-ment. Long delays in crop establishment encouragemore pest generations to develop. Cutworms and


armyworms commonly build-up under these circum-stances and thus are more common in RWR thanirrigated rice. On the other hand, if rice is direct seeded,the early planting reduces time for pest reproduction.RWR farmers commonly state that late plantings leadto increased pest densities. Natural enemies are slowerto colonise, allowing pests to outpace them. Closeproximity to irrigated areas often leads to increasedpest abundance for the more dispersive species such asplanthoppers, leafhoppers, and mirid predators.

In RWR areas it is common for N. nigropictus tooutnumber N. virescens probably due to the former’swider host range and thus survival ability over thefallow period (Ishii-Eiteman and Power 1997). Sogawa(1976) found that green leafhopper peaks, just likebrown planthopper in single crop RWR, were gen-erally more distinct. Long-maturing varieties, commonin RWR, allow exponential leafhopper build-up forfive or more generations under less natural enemypressure than occurs in irrigated double crops. Basedon this evidence and the field sampling in Table 4, thehigh populations of green leafhoppers reported in Sand SE Asia, where direct feeding damage wasreported (Alam 1967; Viswanathan and Kalode1984), can be attributed to extensive single-cropRWR areas sown to highly susceptible traditionalvarieties. Singh and Singh (1985) found that suchvarieties can become ‘hopper burned’ without anyother provocation. Green leafhoppers have become lessimportant with replacement of large tracts of tradi-tional varieties with resistant modern ones.

RWR culture tends to favour vegetative stage pestssuch as whorl maggot and caseworm that undergomore generations from the combination of moreprolonged vegetative periods of longer maturing ricesplus staggered planting. Rice whorl maggot was firstdescribed in the Philippines as a new pest of irrigatedrice in the early 1960s soon after modern rices weredeveloped and was assumed to be a new pest spawnedby irrigated rice culture (Ferino 1968). Modern rices,being higher tillering, provide greater leaf densities toencourage higher populations. Also whorl maggotsurvival is highly benefited by irrigation as fielddrainage is a recommended cultural control method(Litsinger 1994). The possible reason for this isdiscussed in Jahn et al. (2007). Irrigated rice areagreatly expanded with the success of modern varieties;this has created more juxtaposed RWR and irrigatedagroecosystems allowing whorl maggot easy colonisa-tion of RWR. Like whorl maggot, Rivula was identifiedonly after irrigation expanded (Malabuyoc 1977). Forboth Rivula and whorl maggot, their new discoveriesseem surprising in light of their abundance in the threewidely separated RWR sites which means that theyeither: (1) were overlooked, (2) were recent introduc-tions from another country, or (3) seasonally migrateto RWR from irrigated areas. None of these three ricepests was mentioned in the early rice pest literature

prior to the modern rices in the Philippines (Cendanaand Calora 1967).

A preferred caseworm oviposition site is underleaves that lie flat on the water surface, common in thevegetative stage of a rice crop (Litsinger et al. 1994a).This stage bears succulent leaves that facilitate leafrolling, thus traditional rices with their long vegetativeperiods would also favour caseworm development.Caseworm also is highly susceptible to insecticides(Litsinger and Bandong 1992), thus area wide popula-tions become depressed from the extensive chemicalusage common in irrigated rice bowls. The reason whycaseworm was so abundant in the first crop of doublecrop rice in Iloilo was due to the late (July), andtherefore staggered, planting that would allow moregenerations to develop. In the 2 years of late plantings,defoliation averaged 51%, whereas the 2 years withearlier plantings (May and June) the figure was only 7%.Thus, early plantings normally escape damage. Thesecond crop of rice should have had highest densitiesamong all crops as caseworm has few natural enemies(Litsinger et al. 1994c). However, low rainfall typical oflate wet seasons results in intermittent ponding, whichperhaps proved unfavourable to the gill-bearing, semi-aquatic larvae (Litsinger et al. 1994a).

The greenhorned caterpillar, rice skipper, andgrasshoppers are more prevalent in RWR sitesprobably because of lower insecticide pressure than inirrigated rice as was noted in Japan (Kiritani 1992).Both butterfly species diapause thus are highly adaptedto a RWR environment. Greenhorned caterpillars,which aestivate as adults with wings folded during thecrop-free dry season in litter under trees near rice fields,mimic dead leaves and are readily flushed when onewalks past. However, RWR can readily tolerate themoderate defoliation levels they cause during thereproductive rice stage.

Traditional rainfed wetland rices exhibited a higherincidence of stemborer damage than on modernvarieties (Table 2). Because they are photoperiod-sensitive, traditional rices normally sustain five or moregenerations per crop. Also, being tall, they undergo anextended period of stem elongation and thus longervulnerability to first instar larval tiller penetration asprotective silica bodies become less compact withgrowth (Bandong and Litsinger 2005). Traditionalrices are also low tillering, which concentrates attackparticularly among Scirpophaga species where only onelarva per tiller normally occurs.

In the RWR sites, stemborer damage to modernrices was low to moderate thus equivalent to that ofirrigated rice levels but probably for different reasonsthan stated above. Litsinger et al. (2006b) found that,in the asynchronous portion of Koronadal, stemborerswere suppressed due to the sustained pressure from eggparasitoids and predators that also benefited from thecontinuous availability of rice. On the other hand, thelong rice-free period in RWR depressed stemborer


populations particularly if rice stubble is ploughedunder prior to the rainy season as both Scirpophagaspecies lie dormant in the crowns. S. innotata aestivatesthroughout its distribution (Litsinger et al. 2006a),while S. incertulas enters quiescence in locations withcold winters (Islam 1993). In all three RWR sites therewas always a higher ratio of Scirpophaga to non-Scirpophaga stemborers, pointing to Scirpophagaborers as being better adapted to a wetland environ-ment. In dryland rice sites where early maturing ricesare preferred, rice stubble is often ploughed up toestablish a follow-on maize crop killing aestivatinglarvae, but the rice area is smaller than is typical forwetland environments, allowing more non-Scirpophagaborers that multiply on maize and sugarcane tocolonise and concentrate.

Rice leaffolder populations are often highest infields where high N rates were applied as noted inBatangas, a dryland site (Table 8). Ovipositing mothsare attracted to the most vigorous growing fields (deKraker et al. 2000), but the long rice-free dry seasonlimits natural enemy population buildup (Barrion et al.1991). Thus, the high leaffolder damage levels in thefirst RWR crop in Iloilo and Pangasinan (Table 2) wereprobably due to the low initial populations of naturalenemies. Most likely beneficials then increased over theseason to suppress leaffolders in the second crop whereadditionally drought stress limited survivorship fromsuboptimal dietary moisture (Mochida et al. 1987).Tall traditional rices are often sown in the lowest-lying,flood-prone fields that accumulate greater amounts ofalluvium and thus have higher levels of N which couldbe the reason why traditional rice in Iloilo had highleaffolder damage levels.

The highest rice seed bug densities occurred inRWR environments and the lowest in irrigated rice.There are two possible reasons for this: (1) RWR fieldstypically have larger bunds which allow more alter-native hosts to become established and (2) shadedwooded areas, more prevalent in RWR than irrigatedhabitats, serve as a refuge necessary to aestivate.

Brown planthopper numbers were highest in Iloilowhere the mean density of 149/m2 converts to 0.4/tiller(based on 25 hills/m2 and 15 tillers/hill), near to anaction threshold level of 0.5–1/tiller (Litsinger et al.2005). Spider densities of 54/m2 were one-third those ofbrown planthopper. As a spider can kill a mean of fiveplanthoppers per day (Kenmore et al. 1984), naturalenemies were sufficiently abundant to contain thepopulation, thus there was no planthopper-causedhopperburn in our trial plots. The beneficial role ofspiders was underscored in Cagayan after the floodwaters from a large typhoon carried spiders away,resulting in localised hopperburn from immigratingbrown planthoppers (Litsinger et al. 1986).

Data from the literature were used to compareparasitism rates of common rice pests in irrigated sitesin the Philippines and elsewhere in tropical Asia with

our results from the three RWR sites. Of the 17pest 6 life stage comparisons in Table 5 only in fivewere the mean rates of parasitism in RWR higher thanin irrigated rice while in nine the parasitism rates ofirrigated rice were more than twice that of RWR.Interestingly greenhorned and skipper larval parasitismrates in RWR sites exceeded those in irrigatedlocations while those for the egg stage did not. Thesame growth stage reversal of parasitism was truefor Scirpophaga larvae where rates were higher inRWR (particularly in Pangasinan), but those of theegg stage were substantially lower than irrigatedsites. Rates of leaf-/planthopper egg parasitism, as aguild, matched and occasionally exceeded those ofirrigated rice. The explanation for this is egg para-sitoids build up on the many hopper species feeding onweeds and volunteer rice that emerge at the beginningof the rainy season in RWR sites due to delays intransplanting. As egg parasitoids have shorter lifespans than parasitoids that attack nymphs and adults,this does not hold true for pipunculid, Strepsiptera,and dryinids. These results support the generalisationthat natural enemies are more prevalent in irrigatedthan RWR ecosystems.

4.2. Yield losses

Yield losses were both low and high between differentsites within each ecosystem (Table 6). Such differencescan be explained in terms of cultivar type, yieldpotential and crop compensation as well as insectpest abundance. Traditional rices have considerableability to tolerate defoliation, which under certaincircumstances, can even cause a yield increase(Litsinger 2009). That modern rices were unable toout-yield traditional cultivars in Cagayan shows howunfavourable the environment was, oscillating betweendrought and submergence, often repeatedly, within thesame season. But in the two favourable RWR sites,modern rices were successfully grown, achieving muchof their yield potential. Remarkably modern rices evenappear to have greater powers of compensation thantraditional cultivars from not only leaf removal butalso tiller removal (Litsinger et al. 2005, 2006c). Astraditional varieties tiller poorly, loss of tillers cannotbe readily compensated. During the vegetative stage,modern rices have shown no yield loss from up to 50%defoliation (van Haltern 1979) or removal of 30% oftillers (Rubia et al. 1990). Compensation from stem-borer whiteheads (Rubia and Penning de Vries 1990)and rice seed bug damage (Litsinger et al. 1998) canalso be high from a reallocation of photosynthate fromdamaged to undamaged plant parts.

Litsinger (1993) showed that increasing levels ofcrop management resulted in progressively lower lossesin irrigated sites with modern rices. However, compen-sation can be compromised by: (1) early maturing riceswhich do not allow enough time to outgrow the injury,


(2) suboptimal agronomic management, (3) unfavour-able weather, or (4) the number of stresses. Postonet al. (1983), Pinnschmidt et al. (1995)], Litsinger (1991,1993) and Boling et al. (2004) found that losses inmodern rices are exacerbated when more than onestress (biotic or abiotic) affects the same growth stage.Within irrigated sites such as Guimba, high losses wereassociated with the combination of stemborer damageand drought (Litsinger et al. 2006c), while Savary et al.(1994) found the combination of stemborer damageand weediness to be associated with low yields.

RWR inherently suffers from more stresses thanirrigated rice such as drought and submergence.Another reason is that RWR is grown only duringthe wet season where rain is intrinsically linked tocloudy weather that retards solar radiation slowingphotosynthesis. Kenmore et al. (1984) noted hopper-burn from brown planthopper damage occurred moreon cloudy days. In addition nutrient stress is common.RWR farmers in the Philippines use about half thefertiliser dosage of irrigated rice farmers due toincreased risk of crop failure (Barker and Herdt1979; Pineda et al. 1984). Fluctuating paddy waterlevels, typical in RWR environments, result in greaterlosses of applied N (Yoshida 1981).

RWR has relatively high losses during the vegeta-tive stage which in Pangasinan and Iloilo we canattribute to the combined damage from whorl maggotinjury and caseworm defoliation plus physiologicalstress from a number of causes that may differ eachcrop. Aside from those already mentioned we can addtransplanting shock (Jahn et al. 2007). Both whorlmaggot and caseworm attack the newly transplantedcrop at a time when seedling root systems arerecovering from losing root hairs and rootlets. Often,seedlings older than 30 days are transplanted and astransplanters are in a hurry, when the seedlings arejammed into the soil, the long roots invert into a U-shape, being turned upwards, a process which not onlytakes several weeks for the plants to recover but alsolimits tillering that lowers yield potential. We hypothe-sise that the pest abundance 6 crop stress interactionis the reason for the often high vegetative lossesreported in this study. Losses in the other two growthstages are probably the result of stemborer damagewhich was high in many crops, and again compensa-tion would be compromised from any coterminousstresses.

From these results we can make some general-isations regarding the characterisation of losses basedon the dynamic relationship between the intensity ofstresses present that pull yields down versus the crop’sability to compensate from them. Of the six crops inTable 6 with yield losses 420%, two were dryland andone was irrigated. One can note that these crops werenot necessarily those with the highest insect pestpressure. Siniloan and Claveria dryland sites werecharacterised with highly acidic and eroded soils and

under heavy pressure from rats and blast disease. Theinsecticide check method protected the crops from soil-and sown-seed pests, the main insect pest guilds(Litsinger et al. 2009). Applied inorganic fertiliser hadlittle benefit on the poor soils thus compensation waslimited. The one irrigated site in Guimba was served bya dysfunctional small irrigation system with an electricpump which often failed from power outages thusdrought stress was ever-present and stemborer infesta-tion was perennially high. In addition farmers chosethe earliest maturing varieties such as IR58 to sow. Theother three crops were from the RWR ecosystem withall three study sites represented. In Pangasinan andCagayan, the main single transplanted crops registeredhighest losses with both traditional and modernvarieties in the former. The second crop in Iloilo alsosuffered high losses. All of these crops suffered from acombination of high pest pressure and drought stress.Other RWR and irrigated crops suffered high insectpest infestations but did not register highest losses.

Turning to the four crops with lowest yield losses(510%), the Batangas dryland site sown to thetraditional variety was on highly fertile, young volcanicsoils under high inorganic N while both crops inCalauan, an irrigated site, were sown mainly to longermaturing varieties (Litsinger et al. 2005). The directseeded first crops in Pangasinan and Iloilo, whenplanted early, escaped both transplanting shock andinsect pest pressure and were able to avail of thenatural soil fertility from mineralised soil nitrogen builtup over the dry fallow. From these examples we seethat compensation is favoured by minimal crop stressescounterbalanced with good crop management andlonger maturing varieties.

4.3. Chemical control trials

The results showed that, even when applied at lethaldosages, insecticide usage was unprofitable. In fact, useof action thresholds is only marginally profitable inhigher-yielding, irrigated rice (Smith et al. 1988;Litsinger et al. 2005). In RWR, depending on thecrop, about half of the losses came in the vegetativestage (Table 6), while in irrigated rice, losses occurmore or less equally in all three growth stages thatwould require more costly multiple insecticide applica-tions to prevent (Litsinger et al. 2005). However, RWRpresents a greater challenge than irrigated, double-croprice in terms of making chemical control profitableeven if efforts are concentrated to one stage due to: (1)RWR yield potential is significantly lower than inirrigated rice, thus there are lower potential economicbenefits from the same insecticide usage. (2) Non-systemic granular insecticides are less suited to RWRdue to the erratic ponding depths (Bandong andLitsinger 1979). (3) Rainfall can occur at any time toreduce insecticide residual life, whereas in the dryseason irrigated crop is essentially rainfall free.


(4) Farmers using lever-operated, knapsack sprayersdo not apply adequate spray volumes and severelyunderdose. A previous study showed that Filipinofarmers have adopted insecticides because they feelthat they are needed in the same sense that fertiliser isneeded to obtain high yields (Kenmore et al. 1985).Farmers overestimate the threat posed by insect peststhus are fearful of epidemics that they have seen orexperienced (Escalada and Kenmore 1988; Heong1998). These perceptions need to be overcome giventhat insecticide usage in RWR is uneconomical.

4.4. Integrated pest management (IPM)

A greater proportion of RWR crops registered highestpest densities than crops in either dryland or irrigatedecosystems (Table 2). We already discussed some ofthe characteristics of RWR culture that foster greaterproliferation of some of the more common chronicinsect pests based on adaptive strategies of dormancy,polyphagy, and vagility to overcome the long dryfallow of the Asian monsoon climate (Litsinger et al.1987a). Many pests exhibit more than one strategy.Based on comparative abundance, pests show betteradaptation than most of their natural enemies.Among the least adapted pests were brown planthop-per and green leafhoppers [except when juxtaposed toirrigated rice] that achieved only minor pest status ascompared to their acute pest status in irrigated multi-crop rice.

Tungro was long known before the advent ofmodern rices, but it was irrigated rice not RWR thatsuffered more during the hopper/virus epidemics of the1970s and 1980s. Such epidemics were due to thecombined shrinkage of the rice-free fallow allowingpest populations to carry over from crop to crop(Loevinsohn et al. 1988) combined with increased useof insecticides that killed off natural enemies leading toinsecticide resurgence, secondary pest outbreaks, and arapid breakdown of resistant varieties (Gallagher et al.1994). The brown planthopper and tungro/greenleafhopper flare-ups in RWR in Iloilo were probablydue to its close proximity to irrigated areas thatexhibited these causes rather than from indigenouscauses. Based on the analysis of the RWR ecosystem, acontrol strategy for double-cropped, irrigated rice wasdeveloped to create a 2-month, pest suppressive, rice-free period between the dry and wet season crops andto discourage planting more than two rice crops peryear (Litsinger 2008).

The three key pests of RWR in the Philippines werewhorl maggot, caseworm, and Scirpophaga stemborers.Based on the results of this study, an IPM strategy forfavourable RWR areas would be to increase thecompensatory ability of rice by selecting high-tillering,medium-maturing varieties and undertaking goodagronomic management to reduce stresses and mini-mise the use of insecticides to respond only to crop-

threatening attacks. A different strategy is needed forunfavourable areas where varieties are needed thatshare more characteristics with traditional cultivars inorder to best tolerate the extreme stresses that definethis environment. One of the reasons why traditionalrices can provide a reasonable yield even under severestress is their longer maturity which allows more timefor yield compensation to occur. However, as tradi-tional rices lodge when inorganic nitrogen is added,their response to better management is limited.Traditional rices are tall thus are better adapted toperennially flooded rice fields where shorter varietiesmore readily succumb after submergence for a fewdays. But longer maturity also means more insect pestgenerations and higher pest damage. Now breeders areimproving RWR rices in unfavourable environmentsusing taller and longer maturing cultivars (Xu 2006).Bt-rice (Cohen et al. 2000) should increase yieldpotential in both favourable and unfavourable envir-onments against stemborers and caseworm. Stem-borers in particular damage the crop over severalgrowth stages and the type of damage is least able to becompensated in low tillering cultivars by agronomicmanagement. The benefits of Bt-rice in unfavourableenvironments should be higher than recovering just theloss caused directly by stemborers due to synergisticcompensatory effects (Litsinger et al. 2006c).

Acknowledgements

We are indebted to the field work performed by our site staffin Oton Iloilo, Manaoag Pangasinan, and Solana Cagayanwithout whose help this research would not have beenpossible. We are grateful for the assistance of Nonnie Bunyiand Josie Lynn Catindig at IRRI in providing references andtechnical information. In addition the assistance provided bythree anonymous reviewers is gratefully appreciated.

References

Alam MZ. 1967. Insect pests of rice in East Pakistan. In: Themajor insect pests of rice. Baltimore (MD): JohnsHopkins Press. p. 643–655.

Arida GS, Shepard BM. 1990. Parasitism and predation ofrice leaffolders, Marasmia patnalis (Bradley) and Cna-phalocrocis medinalis (Guenee) (Lepidoptera: Pyralidae)in Laguna Province, Philippines. J Agricultural Entomol.7:113–118.

Bandong JP, Canapi BL, dela Cruz CG, Litsinger JA. 2002.Insecticide decision protocols: a case study of untrainedFilipino rice farmers. Crop Protect. 21:803–816.

Bandong JP, Litsinger JA. 1979. Evaluation of granularinsecticides for rainfed wetland rice in the Philippines. IntRice Res Newslett. 4(2):15.

Bandong JP, Litsinger JA. 2005. Rice crop stage suscept-ibility to the rice yellow stemborer Scirpophaga incertulas(Walker) (Lepidoptera: Pyralidae). Int J Pest Manag.51:37–43.

Barker R, Herdt RW. 1979. Rainfed lowland rice as aresearch priority – an economist’s view. p. 3–35. In:Rainfed lowland rice: selected Papers from the 1978International Rice Research Conference. Los Banos(Philippines): IRRI. p. 341.


Barrion AT, Litsinger JA. 1985. A method for holding eggsof rice insect pests for parasite emergence. Int Rice ResNewslett. 10(2):19.

Barrion AT, Litsinger JA, Medina EB, Aguda RM, BandongJP, Pantua PC, Jr, Viajante VD, dela Cruz CG, Vega CR,Soriano JS, Jr, et al. 1991. The rice Cnaphalocrocis andMarasmia (Lepidoptera: Pyralidae) leaffolder complex inthe Philippines: taxonomy, bionomics and control.Philippine Entomol. 8:987–1074.

Boling A, Tuong TP, Jatmiko SY, Burac MA. 2004. Yieldconstraints of rainfed lowland rice in Central Java,Indonesia. Field Crops Res. 90:351–360.

Catling D. 1992. Rice in deep water. Los Banos (Philippines):IRRI. p. 542.

Cendana SM, Calora FB. 1967. Insect pests of rice in thePhilippines. p. 591–613. In: The major insect pests of therice plant. Baltimore (MD): Johns Hopkins Press. p. 729.

Chandra G. 1978. A new cage for rearing hopper parasites.Int Rice Res Newslett. 3(1):12.

Cohen MB, Gould G, Bentur JS. 2000. Bt rice: practical stepsto sustainable use. Int Rice Res Notes. 25:4–10.

deKraker J, RabbingeR, vanHuis A, van Lenteren JC,HeongKL. 2000. Impact of nitrogenous-fertilization on thepopulation dynamics and natural control of rice leaffolders(Lep.: Pyralidae). Int J Pest Manag. 46:225–235.

de Kraker J, van Huis A, Heong KL, van Lenteren JC,Rabbinge R. 1999. Population dynamics of rice leaf-folders (Lepidoptera: Pyralidae) and their natural ene-mies in irrigated rice in the Philippines. Bull EntomolRes. 89:411–421.

DeDatta SK. 1981. Principles and practices of rice produc-tion. New York: John Wiley and Sons. p. 618.

dela Cruz CG, Litsinger JA, Paragna F. 1981. Tillageimplements for soil incorporation of carbofuran granulesin rainfed wetland fields. Int Rice Res Newslett. 6(1):17.

Escalada MM, Kenmore PE. 1988. Communicating inte-grated pest control to rice farmers at the village level.p. 221–228. In: Teng PS, Heong KL, editors. PesticideManagement and Integrated Pest Management in South-east Asia, College Park, MD, US: Consortium forInternational Crop Protection. p. 664.

Ferino M. 1968. The biology and control of the rice leaf-whorl maggot, Hydrellia philippina Ferino (Ephydridae,Diptera). Philippine Agri. 52:332–383.

Fujisaka S. 1990. Rainfed lowland rice: building research onfarmer practice and technical knowledge. Agri EcosysEnviron. 33:57–74.

Gallagher KD, Kenmore PE, Sogawa K. 1994. Judicial use ofinsecticides deter planthopper outbreaks and extend therole of resistant varieties in Southeast Asian rice. p. 599–614. In: Denno RF, Perfect TJ, editors. Planthopperstheir ecology and management. London: Chapman andHall. p. 772.

Garrity DP, Oldeman LR, Morris RA. 1986. Rainfedlowland rice ecosystems: characterization and distribu-tion. p. 3–23. Progress in rainfed lowland rice. Los Banos(Philippines): IRRI. p. 446.

Heinrichs EA, Katanyukul W, Karim ANMR, Misra BC.1986. Management of insect pests in rainfed lowland rice.p. 349–358. In: Progress in rainfed lowland rice. LosBanos (Philippines): IRRI. p. 446.

Heong KL. 1990. Feeding rates of the rice leaf-folder,Cnaphalocrocis medinalis (Lepidoptera: Pyralidae) ondifferent plant stages. J Agri Entomol. 7:81–90.

Heong KL. 1998. IPM in developing countries: progress andconstraints in rice IPM, p. 68–77. In: Zalucki M, Drew R,White G, editors. Proceedings Sixth Australasian AppliedEntomological Research Conference, University ofQueensland, Brisbane, Australia.

IRRI (International Rice Research Institute). 1976. Lowlandrice cropping systems, Cropping Systems Program.p. 375–388. In: Annual Report for 1975. Los Banos(Philippines): IRRI. p. 479.

IRRI. 1977. Environmental description. Cropping SystemsProgram. p. 311–322. In: Annual Report for 1976. LosBanos (Philippines): IRRI. p. 418.

IRRI. 1978. Control and management of insects. p. 215–216. In: Annual Report for 1977. Los Banos (Philip-pines): IRRI.

IRRI. 1979.Controlandmanagementof insects.p. 193–196. In:Annual Report for 1978. Los Banos (Philippines): IRRI.

IRRI. 1980a. Environmental description. Cropping SystemsProgram. p. 379–395. In: Annual Report for 1979. LosBanos (Philippines): IRRI. p. 538.

IRRI. 1980b. Control and management of insects. p. 221–222. In: Annual Report for 1979. Los Banos (Philip-pines): IRRI. p. 538.

IRRI. 1981a. Environmental description. Cropping SystemsProgram. p. 221–222. In: Annual Report for 1980. LosBanos (Philippines): IRRI. p. 467.

IRRI. 1981b. Control and management of insects. p. 197–198. In: Annual Report for 1980. Los Banos (Philip-pines): IRRI. p. 467.

IRRI. 1983. Control and management of insects. p. 192–193. In: Annual Report for 1982. Los Banos (Philip-pines): IRRI.

IRRI. 1985a. International rice research: 25 years ofpartnership. Los Banos (Philippines): IRRI. p. 188.

IRRI. 1985b. Insecticide evaluation for. 1984. EntomologyDepartment. Los Banos (Philippines): IRRI. p. 232.

Islam Z. 1993. Diapause in rice yellow stem borer,Scirpophaga incertulas (Walker) (Lepidoptera: Pyrali-dae), in Bangladesh. J Plant Protect Tropics. 10:163–175.

Ishii-Eiteman MJ, Power AG. 1997. Response of green riceleafhoppers to rice-planting practices in NorthernThailand. Ecol Appli. 7:194–208.

Jahn GC, Litsinger JA, Chen Y, Barrion AT. 2007.Integrated pest management of rice: ecological concepts.p. 315–366. In: Koul O, Cuperus GW, editors. Ecologi-cally based integrated pest management. Wallingford(UK): CAB International. p. 462.

Kalode MB, Karim ANMR, Pongprasert S, Heinrichs EA.1986. Varietal improvement and resistance to insect pests.p. 241–252. In: Progress in rainfed lowland rice. LosBanos (Philippines): IRRI. p. 446.

Kenmore PE, Carino FO, Perez CA, Dyck VA, GutierrezAP. 1984. Population regulation of the rice brownplanthopper (Nilaparvata lugens Stal) within rice fieldsin the Philippines. J Plant Protect Tropics. 1:19–37.

Kenmore PE, Heong KL, Putter CA. 1985. Political, socialand perceptual aspects of integrated pest managementprogrammes. In: Lee BS, Loke WH, Heong KL, editors.Proceedings of a Seminar on Integrated Pest Manage-ment in Malaysia. p. 47–67. Malaysian Plant ProtectionSociety, Kuala Lumpur.

Kiritani K. 1992. Prospects for integrated pest managementin rice cultivation. Jap Agri Res Quart. 26:81–87.

Litsinger JA. 1979. Major insect pests of rainfed wetland ricein tropical Asia. Int Rice Res Newslett. 4(2):14–15.

Litsinger JA. 1991. Crop loss assessment in rice. p. 1–65. In:Heinrichs EA, Miller TA, editors. Rice insects: manage-ment strategies. New York: Springer-Verlag.

Litsinger JA. 1993. A farming systems approach to insect pestmanagement foruplandand lowland rice farmers in tropicalAsia. p. 45–101. In: Altieri MA, editor. Crop protectionstrategies for subsistence farmers.Westview studies in insectbiology. Boulder (CO): Westview Press. p. 197.


Litsinger JA. 1994. Cultural, mechanical, and physicalcontrol of rice insects. p. 549–584. In: Heinrichs EA,editor. Biology and management of rice insects. NewDelhi: Wiley Eastern Ltd. p. 779.

Litsinger JA. 2008. Areawide rice insect pest management: aperspective of experiences in Asia. p. 351–440. In: KoulO, Cuperus G, Elliott N, editors. Areawide pest manage-ment: theory and implementation. Wallingford (UK):CABI. p. 590.

Litsinger JA. 2009. When is a rice insect a pest yield loss andthe Green Revolution. p. 391–498. In: Peshin R, DhawanAK, editors. Integrated pest management: innovation-development process. Berlin: Springer Science þ MediaB.V., Vol 1, p. 670.

Litsinger JA, Alviola AL, Canapi BL. 1986. Effects offlooding on insect pests and spiders in a rainfed riceenvironment. Int Rice Res Newslett. 11(5):25–26.

Litsinger JA, Alviola AL, dela Cruz CG, Canapi BL,Batay-an EH, III, Barrion AT. 2006a. Rice whitestemborer Scirpophaga innotata (Walker) in southernMindanao, Philippines. I. Supplantation of yellowstemborer S. incertulas (Walker) and pest status. Int JPest Manag. 52:11–21.

Litsinger JA, Alviola AL, dela Cruz CG, Canapi BL,Batay-an EH, III, Barrion AT. 2006b. Rice whitestemborer Scirpophaga innotata (Walker) in southernMindanao, Philippines. II. Synchrony of planting andnatural enemies. Int J Pest Manag. 52:23–27.

Litsinger JA, Bandong JP. 1992. Response of the ricecaseworm Nymphula depunctalis (Guenee) to insecticides.J Plant Protect Tropics. 9:169–177.

Litsinger JA, Bandong JP, Chantaraprapha N. 1994a. Massrearing, larval behaviour, and effects of plant age on therice caseworm Nymphula depunctalis (Guenee) (Lepidop-tera: Pyralidae). Crop Protect. 13:494–502.

Litsinger JA, Bandong JP, Canapi BL, dela Cruz CG,Pantua PC, Alviola AL, III, Batay-an E. 2005.Evaluation of action thresholds against chronic insectpests of rice in the Philippines: I. Less frequentlyoccurring pests and overall assessment. Int J PestManag. 51:45–61.

Litsinger JA, Bandong JP, Canapi BL, dela Cruz CG, PantuaPC, Alviola AL, III, Batay-an E. 2006c. Evaluation ofaction thresholds against chronic insect pests of rice inthe Philippines: IV. Stemborers. Int J Pest Manag.52:194–207.

Litsinger JA, Barrion AT, Bumroongsri V, Morrill WL,Sarnthoy O. 1997. Natural enemies of the rice green-horned caterpillar Melanitis leda ismene Cramer (Lepi-doptera: Satyridae) and rice skipper Pelopidas mathiasFabricius (Lepidoptera: Hesperiidae) in the Philippines.Philippine Entomol. 11:151–181.

Litsinger JA, Barrion AT, Dandi Soekarna. 1987a. Uplandrice insect pests: their ecology, importance, and control.IRRI Research Paper Series No. 123:1–41 p.

Litsinger JA, Bumroongsri V, Morrill WL, Sarnthoy O. 1993.Rearing, ovipositional biology, and plant host range ofthe rice greenhorned caterpillar Melanitis leda ismeneCramer (Lepidoptera: Satyridae). J Plant Protect Tro-pics. 10:205–218.

Litsinger JA, Bumroongsri V, Morrill WL, Sarnthoy O.1994b. Mass rearing, developmental biology, andhost plant range of the rice skipper Pelopidas mathiasF. (Lepidoptera: Hesperiidae. Insect Sci Appli. 15:9–17.

Litsinger JA, Canapi BL, Alviola AL. 1982. Farmerperception and control of rice pests in Solana, CagayanValley, a pre-green revolution area of the Philippines.Philippine Entomologist. 5:373–383.

Litsinger JA, Canapi BL, Bandong JP, dela Cruz CG,Apostol RF, Pantua PC, Lumaban MD, Alviola AL, III,Raymundo F, Libetario EM, et al. 1987b. Rice crop lossfrom insect pests in wetland and dryland environments ofAsia with emphasis on the Philippines. Insect Sci Appli.8:677–692.

Litsinger JA, Chantaraprapha N, Bandong JP, Barrion AT.1994c. Natural enemies of the rice caseworm Nymphuladepunctalis (Guenee) (Lepidoptera: Pyralidae). Insect SciAppli. 15:261–268.

Litsinger JA, Entomology Department. 1979. An inexpensivekerosene light trap to monitor rice insects. Int Rice ResNewslett. 4(2):17.

Litsinger JA, Gyawali BK, Wilde GE. 1998. Feedingbehaviour of the rice bug Leptocorisa oratorius (F.)(Hemiptera: Alydidae). J Plant Protect Tropics. 11:23–35.

Litsinger JA, Libetario EM, Barrion AT, Apostol RP. 2009.Insect pest complex, yield loss, and response to improvedmanagement of dryland rice in the Philippines. Int J PestManag. 55:129–149.

Litsinger JA, Lumaban MD, Bandong JP, Pantua PC,Barrion AT, Apostol RF, Ruhendi. 1980a. A methodol-ogy for determining insect control recommendations.IRRI Research Paper Series No. 46:1–31.

Litsinger JA, Price EC, Herrera RT. 1980b. Small farmer pestcontrol practices for rainfed rice, corn, and grain legumesin three Philippine provinces. Philippine Entomol. 4:65–86.

Loevinsohn ME, Litsinger JA, Heinrichs EA. 1988. Riceinsect pests and agricultural change. p. 161–182. In:Harris MK, Rogers CE, editors. The entomology ofindigenous and naturalized systems in agriculture.Boulder (CO): Westview Press.

Mackill DJ. 1986. Varietal improvement for rainfed low landrice in South and Southeast Asia: results of a survey.p. 115–144. In: Progress in rainfed lowland rice. LosBanos (Philippines): IRRI. p. 446.

Malabuyoc LA. 1977. A new lepidopterous pest of rice. IntRice Res Newslett. 2(2):6.

Mochida OM, Joshi RC, Litsinger JA. 1987. Climatic factorsaffecting the occurrence of insect pests. p. 149–164. In:Weather and rice. Los Banos (Philippines): IRRI. p. 323.

Morris RA, Patanothai A, Syarifuddin A, Carangal VR.1986. Cropping systems for rainfed lowland rice environ-ments. p. 59–76. In: Progress in rainfed lowland rice. LosBanos (Philippines): IRRI. p. 446.

Pantua PC, Litsinger JA. 1984. Life history and plant hostrange of the rice green semilooper. Int Rice Res Newslett.9(1):26.

Pena N, Shepard M. 1986. Seasonal incidence ofparasitism of brown planthopper Nilaparvata lugens(Homoptera: Delphacidae), green leafhopper Nephotettixspp. (Homoptera: Cicadellidae), and whitebackedplanthoppper Sogatella furcifera (Homoptera: Delphaci-dae) in Laguna province, Philippines. Environ Entomol.15:263–267.

Pineda R, Duff B, Heinrichs EA, Carbonell P. 1984. Insectcontrol practices on irrigated and rainfed rice farms inNueva Ecija, Philippines. Working Paper No. 102. TheConsequences of Small Rice Farm MechanizationProject, International Rice Research Institute, LosBanos, Philippines. p. 24.

Pinnschmidt HO, Batchelor WD, Teng PS. 1995. Simulationof multiple species pest damage in rice using CERES-rice.Agric Sys. 48:193–222.

Poston FL, Pedigo LP, Welch SM. 1983. Economic injurylevels: reality and practicality. Bull Entomol Soc Am.29:49–53.


Rothschild GHL. 1970. Parasites of rice stemborers inSarawak (Malaysian Borneo). Entomophaga. 15:21–51.

Rubia EG, Penning de Vries FWT. 1990. Simulation of yieldreduction caused by stem borers in rice. J Plant ProtectTropics. 7:87–102.

Rubia EG, Shepard BM, Yambao EB, Ingram KT, Arida GS,Penning de Vries F. 1990. Stem borer damage and grainyield of flooded rice. J Plant Protect Tropics. 6:205–211.

Savary S, Elazequi FA, Moody K, Litsinger JA, Teng PS.1994. Characterization of rice cropping practices andmultiple pest systems in the Philippines. Agri Sys. 46:385–408.

Shepard BM, Arida GS. 1986. Parasitism and predation ofyellow stem borer, Scirpophaga incertulas (Walker)Lepidoptera: Pyralidae) eggs in transplanted and direct-seeded rice. J Entomol Sci. 21:26–32.

Singh BN, Singh R. 1985. Hopper burn and varietalsusceptibility of different rice varieties to green leaf hopperunder field conditions. Ind J Entomol. 47:220–222.

Smith J, Litsinger JA, Bandong JP, Lumaban MD, dela CruzCG. 1988. Economic thresholds for insecticide applica-tion to rice: profitability and risk analysis to Filipinofarmers. J Plant Protect Tropics. 6:67–87.

Sogawa K. 1976. Rice tungro virus and its vectors in tropicalAsia. Rev Plant Protect Res. 9:21–46.

van den Berg H, Shepard BM, Litsinger JA, Pantua PC.1988. Impact of predators and parasitoids on the eggs ofRivula atimeta, Naranga aenescens (Lepidoptera: Noctui-dae) and Hydrellia philippina (Diptera: Ephydridae) inrice. J Plant Protect Tropics. 5:103–108.

van Haltern P. 1979. The insect pest complex and relatedproblems of lowland rice cultivation in South Sulawesi,Indonesia. Mededelingen Landbouwhogeschool, Wagen-ingen, Netherlands. 79(1):1–111.

Venugopal MS, Litsinger JA. 1984. Effect of carbofuran onrice growth. Protect Ecol. 7:313–317.

Viswanathan K, Kalode MB. 1984. Comparative study onvarietal resistance to rice green leafhoppers Nephotettixvirescens (Distant) and N. nigropictus (Stal). Proc IndAcad Sci (Animal Sci.). 93:55–63.

Xu K, Xu X, Fukao P, Canlas R, Maghirang-Rodriguez R,Heuer S, Ismail AM, Bailey-Serres J, Ronald PC, MackillDJ. 2006. Sub1 A is an ethylene-response-factor-like genethat confers submergence tolerance. Nature. 442:705–708.

Yoshida S. 1981. Fundamentals of rice crop science. LosBanos (Philippines): IRRI. p. 269.

Zandstra HG, Price EC, Litsinger JA, Morris RA. 1981. Amethodology for on-farm cropping systems research. LosBanos (Philippines): IRRI. p. 149.


Insect Pests of Rainfed Wetland Rice

Documents