CONTROL OF STORED GRAIN INSECTS IN CYPRUSnews.ari.gov.cy/publications/tb20-iordanou.pdf · For T, castaneum : fenitrothion > pirimiphos-methyl > tetra- chlor~~inphos=malathion, and

TECHNICAL BULLETIN 20

CONTROL OF STORED GRAIN INSECTS IN CYPRUS

AGRICULTURAL RESEARCH INSTITUTE

MINISTRY OF ACiRICULTURE AND NATURAL RESOURCES

NICOSIA CYPRUS

NOVEM BEK 1976

CONTROL OF S O R E D GRAIN MSE4XS IN CYPRUS

N. IORDANOU '

AGRICULTURAL RESEARCH INSTITUTE, NICOSIA, CYPRUS

ABSTRACT

In laboratory tests, one month old residues of malathion, bromophos. pirimiphos-methyl, tetrachlorvinfos and fenitrothion applied at the rate of 12 ppm to hard wheat against Rhyzopertha dominica (F), Tribolium castaneum (Herbsd) and Trogoderma granarium Everts, generally effecti\ely controlled all three insects after a 72-hour exposure to treated grain.

The insecticidal efficiency of five organophosphorus insecticides against Sitophilus granarius L., T. granarium, T. castuneunr and Oryzoephilrrs surinamensis L. was evaluated by direct application of spray solutions with a Potter tower in the laboratory. The order of effectiveness at LD50 for S. granarius was : feni- trothion > phoxim > pirimiphos-methyl > malathion > tetrachlorvinphos. For T. granarium larvae : fenitrothion > phoxim z pirimiphos-meth>l> malathion > tetrachlorvinphos. For T, castaneum : fenitrothion > pirimiphos-methyl > tetra- chlor~~inphos=malathion, and for 0, surinamensis : fenitrothion > malathion > phoxim > pirimiphos-methyl > tetrachorvinphos.

The susceptibility of selected wheat varieties to R. dominica was also studied. The aestivum varieties Lahish, Tobari 66 and Safed Lerma were more resistant while other aestivum wheat varieties like Hazera 2152/5104, Blue Silver and Mexipak proved more susceptible to R. dominica than the durum wheat varieties Kyperounda and Capeiti 8.

One hundred per cent kill of both caged and free-flying adults of Plodia inter- punctelia Hbn. and Sirorroga cereuleNu Olivier was obtained in a store filled with barley heavily infested with both pests following space treatment with dichlorvos at the rate of 0.1 g a.i./m3. In a second store with a similar infestation, repeated daily applications of dichlorvos for a period of 40 days, resulted in the elimination of both lepidopterous insects.

r l Satisfactory results were obtained by applying iodofenbs at the rate of

I g a.i./mz one week prior to grain storage in the interior of a store heavily infested with T, granarium larvae. Effective reduction of insect infestation during storage was achieved when iodofenphos wall treatment was supplemented with malathion dust grain treatment at 10 ppm.

Aluminum phosphide applied as Phostoxin(~) tablets at the rate of one 3g- tablet (56% phosphine) per m3 resulted in complete control of a wide range of free living and caged laboratory-bred insect species infesting stored barley 72 hours after treatment.

Malathion or bromophos wall treatments were inadequate to protect stored grain from insect attack unless supplemented with malathion grain treatment.

(1) Agricultunl Research Officer.

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INTRODUCTION

Stored grain all over the world suffers considerable losses from insects which have adapted to a diet consisting of stored products (Parkin 1959). Due to their small size many of these species have been carried extensively through grain trading and have become cosmopolitan.

In tropical countries such grain losses are more serious than in other regions because of high year-round temperatures and inadequate storage facilities. High grain moisture content also favours the survival and reproduction of stored grain insects. (Cotton er al. 1960).

Actual losses sustained are rather difficult to estimate. Insects may damage stored grain by feeding on it, lowering its germination and milling quality, spoiling its appearance, causing it to heat and by creating conditions favourable for the development of moulds (Parkin 56, Howe 65).

Methods of grain storage and protection from insect attacks have evolved from primitive (Fletcher and Ghosh 1920, Pruthi 1949) to modern which include hygiene, sealed storage (Hyde 1962), non-radiant heat, radiant energy, fumigation, mechanical means and contact insecticides. Literature on the subject is voluminous e .g . chemical control of stored grain insects (Parkin 3956), special problems in individual countries (Proctor and Ashman 1972), description of control methods of insects in particular products (Watters 1968, Spitler and Harstell 1969, Green and Tyler 1966) or with particular insecticides (McFarlane 1961, Lemon 1966, 1967, Strong and Sbur 1960, 1964, Lemon 1967, McDonald and Gillenwater 1967, Strong 1970 etc.)

In Cyprus, stored grain insect infestations occur frequently in outbreak pro- portions because of favourable climatic conditions (high temperatures throughout most of the year) and the lack of effective means of control. In some years above- average harvests force grain producers anti handlers to use many types of t emporag storage especially old houses made of hard bricks or sun-baked earth bricks which are usually unsuitable for storing grain. This temporary storage always causes entomological problems. The annual production of the country is collected and stored in Communal Cooperatire stores for a period of 4 to 8 months prior to its delivery to the Central Cooperative Stores in the main towns of the country. As a standard practice, empty stores are treated prior to grain storage with malathion a t the rate of 1.25 g a.i. per square meter. This treatment is recommended for all Communal and Central Cooperative stores. In cases, however, where empty rooms or small stores in farmer's dwellings are used for temporary storage this treatment is not always applied.

The insect species at'lcking stored grain in Cyprus, their relative importance and the degree of damage they cause have already been reported (Iordanou 1970 a) ; also reported are preliminary tests on the chemical control of these insects in the laboratory and in the store (lordanou 1970 b).

Under Cyprus conditions it was realised that most insect infestations in stored grain originate during temporary storage in untreated small stores ; grain infested in this way is then transferred to Cooperative Stores which have their interior surfaces treated with insecticides, since nevertheless insects feed in the grain heaps, they do not necessarily come into contact with treated surfaces and escape control (Iordanou 1970 b).

4

Based on the information obtained on the insect species affecting stored grain in Cyprus, mode of infestation and grain weight losses, further laboratory and field trials were conducted in order to find effective means of chemical control.

MATERIALS AND METHODS

Laboratory Studies-Grain Treatment .- The effectiveness of a number of low mammalian toxicity organophosphorus

insecticides, namely malathion, bromophos, pirimiphos-methyl, tetrachlorvinphos, iodofenfos and fenitrothion was studied in the laboratory against adult insects of R. dominica and Tribolium castaneum Hbst. and against larvae of 7. granarium. Insecticides dissolved in water, were applied on hard wheat at the rate of 12 ppm witha constant pressure grain spraler. Treated grain was kept at room temperature in plastic buckets in the laboratory after thorough agitation for five minutes. Experimental insects were obtained from cultures kept in the laboratory. T. castaneum was reared on wheat flour enriched with 5 % brewers yeast, T. granarium larvae on whole barley kernels and R. dominica on whole wheat kernels. The effectiveness and residual life of test insecticides was determined by monthly assays. Experiments were replicated three times. A total of sixty insects of each species were used in each assay. Each batch of insects was exposed to 300 g of treated grain in 425 cc glass jars. Mortality records were taken after 24, 48 and 72 hours of exposure for R. dominica and 72 hours for the other two species. Insects were recorded as dead if they did not show any signs of mo\ement.

The first bioassay test was made one month after the insecticide grain treat- ments. When 3. dominica was used as test insect, the effectiveness of insecticides was studied for a period of two months from initial application. With T. castaneum and T. granarium however, tests were made over a period of six consecutive months.

Insect Treatment .- Further insecticide screening trials were conducted against a number of

laboratory bred stored grain insects in 1972. The insects S. gronarius, T. granarium, T. castaneum and 0. surinamensis of the Cyprus strain and the insects T. castaneum and Tribolium confusum J. du Val. of the English strain were used as test insects. All species were tested in the adult stage except for T. granarium which was tested in the third larval instar. A total of sixty insects were used in each treatment in a three times replicated experiment.

The following low mammalian toxicity organophosphorus insecticides were tested in the emulsion form : malathion, phoxim, fenitrothion, pirimiphos-methyl and tetrachlorvinphos. The formulated insecticides were diluted in distilled water to the desired concentration. Tests with each chemical included a control con- sisting of the application of the solvent (distilled water) alone. The range of con- centrations to be used was determined separately for each chemical by running preliminary or range finding trials.

The solution of the different insecticides were applied to the test insects with the fine nozzle of an S.T.4 Burkard Potter precision laboratory spray tower. The spray tower was modified slightly to prevent contamination o f the toxicology labo- ratory and to eliminate hazard to the operator. All four sides of the apparatus were covered with plexiglass. A plexiglass door was also fitted to the lower front side of the tower in order to permit easy access to the spray table. An exhaust fan, specially designed for this use, was installed at the lower left side of the apparatus. The exhaust fan was equipped with a shut-off gate which was kept closed when

5

the spray tower was in operation and opened at the end of each insecticide treatment. A bigger exhaust fan was also installed at the top of a side wall of the toxicology laboratory. This was in continuous operation when the spray tower was in use for constant air exchange in the toxicology laboratory.

The spray tower was calibrated so that the distribution of the spray droplets on the table was as uniform as possible. Air pressure was maintained a t 8 lb/inchz for as many seconds as were required for the application of 1 ml of aliquot of spray solution. An additional 30-second settling period was allowed before the insects were remo\ed from the spray tower. Before each test experimental insects in batches of 20 were anaesthetized in 28.5 cc vials with CO, for approximately one minute. The anaesthetized insects were placed in the center of a rectangular (17x 17 cm) typewriter paper covering an area of a circle approximately 5 cm in diameter. Care was taken so that no insects were touching each other. The paper was discarded after each spray. Control insects were treated a t the beginning of each test with I ml of distilled water. These were held under the same conditions as the rest of the treated insects. After the application of the highest concentration of each test insecticide the spray tower was cleaned by flushing the reservoir, nozzle and spray tube several times with acetone before testing another insecticide. After treatment, experimental insects were held in the same glass containers used for the anaesthetization. When 0. surinamensis was the experimental insect the upper part of the glass vials was dipped to a depth of 3 cm in flu on(^) (Polytetrafluore- thylene dispersion I.C.I.) to prevent the insects from climbing and escaping from the vials. No food was placed in the vials. The lids of the glass vials were modified for aeration of the insects. A 2 cm hole was drilled in the center of the lid and a piece of organdy was glued onto it.

After each test glass vials containing experimental insects were held in an illuminated incubator at 25°C and 50 to 55% R.H. for 24 hours before morta- lities were recorded. Insects were recorded as dead if they did not show any signs of movement. Corrections for the negligible natural mortality observed in controls were made by using Abott's formula (Abott 1925).

Susceptibility of Selected Wheat Varieties to the Lesser Grain Borer, R. domonica.- The susceptibility of four wheat varieties to R. dominica attack was studied

in the laboratory in 1974. The varieties tested were the durum wheats (Triticum durum), Kyperounda and Capeiti 8 and the bread wheats (Triricum aestivu~n), Pitic 62 and Lahish. Two hundred grams of grain from each variety were placed in 425 cc glass jars and exposed to I00 adults of R. doniinica for a period of 3 lj2 months in an experiment replicated four times. Jars were held during the feeding period in an incubator a t 25" C and 65 % R.H. Records of grain weight losses and increase in insect numbers were taken a t the end of the exposure period.

The susceptibility of additional wheat varieties was tested in early 1975. The new varieties tested were Tobari 66, Hazera 2152/5104, Safed Lerma, Blue Silver and Mexipak 69 ; Kyperounda and Capeiti 8 were tested again. The experimenial procedure was slightly modified. Thus, 50 R. donlinica adults were used and the exposure period was increased to 4 months.

Field Trials.-I. Effectiveness of Dichlorvos Against Lepidopterous Pests of Stored Grain.- The insecticidal value of dichlorvos against lepidopterous stored grain pests

was studied in two locations, namely, Trikomo and Kormakitis and in 1971 and 1972 respectively.

(a) Trikomo Trial :-Test was conducted in an old store at Trikomo on wheat heavily infested with Angumois grain moth, S. cerealella and the Indian meal moth P. interpunctella. The insecticide dichlorvos (as VAPONA (R)) was tested in mid October at 0.1 g a.i./m3 with the aid of a Fontan (R) low volume sprayer. The insecticide was dissolved in water a t 5 ml a.i.1500 ml water in order to facilitate the flow of the chemical through the No. 18 nozzle of the sprayer. Insecticide cloud was directed to all parts of the interior of the store. After insecticide application all windows and doors were shut. Adults of both species were collected from the store prior to insecticide application and were placed in 10 small cages in hatches of 50 (25 adults of each species). Caged insects of both species were placed as uniformly as possible back to the store two hours after treatment in order to study the fumigant action of the test chemical. Appraisal of results was based on mortality of caged and free flying insects of both species.

Two additional dichlorvos spray applications were made in the same store at 18-day intervals.

(b) Kormakitis trial :- This test was conducted on barley heavily infested with P, inrtrpunctella and

S. cereulella in a cooperative store at Kormakitis in September 1972. Dichlorvos was again tested at 0.1 g a.i./m3 using a Fontan (R) low volume sprayer. The insecticide was applied daily late in the afternoon for 40 consecutive days. Eight square, metal, sticky traps (30.48 by 30.48 cm) were placed in the experimental store to detect moth flying during the experiment as follows : Two on each of the interior walls and two on top of the grain bulk.

The first spray was applied on 2lst September and sticky traps were placed in the store 8 days later. Sticky trap catch records were taken at weekly intervals and continued for a period of 6 weeks after the termination of spray. Two adjacent stores were also treated with dichlorvos periodically in order to prevent reinfestation of the experimental store.

11. Effectiveness of Iodofenphos Wall Treatment Supplemented by Malathion Grain Treatment .- Iodofenphos (as Nuvanol N (R)) was tested as empty store disinfectant in a

store heavily infested with Khapra bettle, T. grunarium, larvae at Aradippou. The test insecticide was applied in the middle of June, approximately one week prior to barley storage, with the aid of a Holder high pressure sprayer at the rate of 1 g a.i./ma to all interior surfaces of the store, as a 2.5% a.i, wettable powder solution. Following application all doors and windows of the store were kept open for two days in order to speed up evaporation of excess moisture from the interior of the store. Immediately before grain storage a thin layer of insecticidal dust was spread on the floor of the store. During the processing of storing, grain was admixed with malathion 2% D at the rate of half a kilogram per ton (10 ppm). The insecticide admixture of grain continued until the store was approximately 213 full. The remaining 113 of stored barley was not admixed with malathion for comparison of the degree of infestation of the two lots during storage.

Grain samplings were made at monthly intervals for a period of ten consecutive months, with the aid of a 183 cm sectional spear sampler. Samples of stored barley were taken by mixing five separate and randomly picked samples. Live insects were extracted from the sample with a No. 12 sieve*. Grain moisture content was determined in the laboratory by drying a sample for 24 hours to constant weight a t 100" C.

This ia based on the U.S. Standard Sieve Series.

111. Effectiveness of Aluminum Phosphide.- Aluminum phosphide, applied as Phostoxin (R) tablets was tested against a

wide range of stored grain insects infesting bagged barley in a 16 mS store. Grain samples taken from the infested stock prior to fumigation showed that

it was heavily infested with 0, surinamensis, Tribolium spp., T. granarium larvae, R. dominica and the flour mite Acarus siro L

Four laboratory bred insects species, namely S. oryzae, R. dominica, T. castaneum adults and T. ~ranarium larvae were also used as test insects in an experiment replicated four times. Insects were placed in 425 cc glass jars in batches of 25 without food. Jars were covered with organdy to prevent escape of test insects and were randomly placed on the floor of the store prior to fumigation among the bags of barley.

Each 3 g Phostoxin (R) tablet contained 56% phosphine. The dosage rate was 1 tablet per ma. Tablets, in batches of two, were placed in 10 cm diameter petri dishes on top of bagged barley. Self adhesive PVC tape was used to seal the door of the store, which was left closed for 72 hours after which period it was aerated with an electric fan for 30 minutes. Live and dead experimental insects were then counted.

IV, Insecticidal Value of Malathion or Bromophos Wall Treatments and Malathion Wall and Grain Treatments Against Stored Grain Insect Attack.- Three cooperative stores located in three villages of the Nicosia district were

used for this trial. The first two received malathion or bromophos wall treatments only applied one week prior to grain storage on all interior surfaces. The third store received malathion wall treatment supplemented by malathion grain treatment.

Malathion and bromophos wall treatments were applied at the rates of 1.25 and 1.0 g a.i./m2 respectively in the interior surfaces of the stores with the aid of a Holder (R) high pressure sprayer.

Malathion dust grain treatment was applied during unloading process and storing by admixing 2% insecticide dust with grain at the rate of 112 kg per ton (10 P P ~ ) .

Grain samples were taken at monthly intervals thereafter. Live insects were extracted from the sample with a No. 12 sieve. Records on live insects in the interior of stores were also taken.

RESULTS AND DlSCUSSlON

Laboratory Studies -Grain Treatment .- The results of the bioassay tests with R. dominica are shown in Fig. 1. At the 24-hours exposure period, one month after treatment the most effective

insecticides were tetrachlorvinphos, in all three forms, followed by fenitrothion and pirimiphos-methyl in the dust form. Somewhat less effective were the insecticides pirimiphos-methyl, malathion and bromophos in the emulsion form. The remaining insecticides caused less than 30% mortality.

At the 48-hour exposure period all forms of tetrachlorvinphos and pirimiphos- methyl dust gave 100% mortality. Malathion dust, pirimiphos-methyl, bromophos and malathion emulsion gave over 70% mortality. The rest of the test insecticides gave less than 50% mortality.

At the 72-hour exposure period all insecticides, except bromophos in the dust form, gave over 83% mortality.

8

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Fig. 1. Monality in the laboratory of R. dotninica adults after exposure for 24. 48 or 72 hours

to grain treated with insecticide, at indicated month after treatment.

Two months after treatment all three tetrachlorvinphos formulations gave the best results at all three exposure periods. At the 48-hours exposure period malathion i n the dust from was the second most effective chemical followed by fenitrothion and malathion emulsion. Similar results were obtained a t the 72-hour exposure period. Bromophos dust was the least effective chemical. Poor results were also obtained with iodofenfos.

Fig. 2. Mortality in the laboratory of T. collmuum adults nfrer exposure for 72 houn to t rnred grain, at indicated month afrer treatment.

Figure 2 shows the results a t 72-hour exposure period obtained when T. castaneum was the test insect. All insecticide treatments gave over 93 % mortality one month after treatment. At the second month, mortalities were still very high. The most effective chemicals were pirimiphos-methyl in both the emulsion and dust forms and fenitrothion emulsion. Both chemicals caused 100% mortality. Statistically similar results were obtained with both formulations of malathion,

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iodofenphos and tetrachlorvinphos in the wettable powder form. In the remaining four months of tests, pirimiphos-methyl and fenitrothion were the most persistent chemicals. At the third month the two malathion formulations, all three forms of tetrachlorvinphos and iodofenphos in both forms were equally effective. Bromophos however, had lost its insecticidal action. For the fourth month and thereafter all insecticide treatments except pirimiphos-methyl and fenitrothion lost most of their action.

Somewhat similar results were obtained with T. granarium larvae (Fig. 3). Pirirniphos-methql in both forms and fenitrothion proved the most persistent chemicals whereas tetrachlorvinphos was effective for two months and the rest of test insecticides were effective the first month only. Fenitrothion was signi- ficantly less effective than pirimiphos-methyl at the fifth and sixth month. The rest of the chemicals practically lost their insecticidal action by the fourth month.

Similar results were obtained by La Hue (1975) with pirimiphos-methyl applied as a water emulsion to hard winter wheat and shelled yellow corn. One hundred per cent kill of all exposed adults of S. oryrae. I. castaneum, I . confusum and R. dominica was obtained. He also reported that malathion applied at the rate of 10 ppm ga,e complete protection to both grains for three months. Satisfactory results with pirimiphos-methll were also obtained by Soderstrom and Armstrong (1975) against T. castaneum, 0. surinamensis and P. interpunctella infesting stored raisins. At the lowest concentration tested (2 ppm) pirimiphos-methyl protected stored raisins for 12 months.

As regards the effectiveness of malathion, Strong and Sbur (1960) reported that 100 per cent mortality of T. granarium larvae was obtained after exposure for 28 days to wheat treated with 10 ppm of malathion. They later also reported that malathion was equally effective against S. oryzae and R. dominica (Strong and Sbur 1 964).

Insect Treatment.- Data in Table 1, show the relative susceptibility of S. granarius, T. granarium.

T. castaneum and 0. surinamensis all of the Cyprus strain (CY) and of T. castaneum and T. confusum of the English strain (G.B.) to five insecticides, including malathion which served as standard. The differences in susceptibility are indicated by LD50 and LD9S values obtained 24 hours after treatment.

Fenitrothion was the most effective insecticide against all insect species tested followed by phoxim. Phoxim, nevertheless, in the specific case of T. confusum (G.B.) was superior only to malathion. Pirimiphos-methyl rated third in effective- ness and tetrachlorvinphos and malathion were the least effective. Tetrachlorvinphos was however effective against T. confusum (G.B.) being in this instance inferior only to fenitrothion.

With respect to susceptibility, the insect species tested responded uniformly to phoxim, pirimiphos-methyl and malathion but differently to fenitrothion and tetrachlorvinphos. The order of susceptibility for the first three insecticides was T. castaneum (GB) > T. castaneum (CY)=T. granarium (CY) > S. granarius (CY) > T. confusum (GB) and > 0. surinamensis (CY). For fenitrothion the order of suscepti- bility was : S. granarius (CY)=T. granarium (CY) > T. castaneum (GB) > T. castaneum (CY) > 0. surinamensis (CY) > T. confusum. Finally for tetrachlorvinphos: T, castaneum (GB) >T. confusum (GB) >T. castanem (CY) >T. granarium (CY)> 0. surinamensis (CY) and > S. granarius (CY) which was practically immune t o this chemical.

M o n t h s a f t e r t reatment

The results obtained in these tests were similar with those obtained by other workers elsewhere. Thus Lemon (1966) working on the effectiveness of 16 organo- phosphorus insecticides against T. carlaneurn and T. confusurn and using the topical application technique reported that fenitrothion was more effective than malathion against both insects. In further tests (Lemon 1967) he also reported that fenitrothion

Ftg. 3. Mortality in the labontory of T. panmiurn larvae aker erpaure for 72 hours to treated grain. at indicated month after treatment.

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was the most effective chemical of the three insecticides tested namelv malathion, hromophoc and fenitroth~on ag;~in\t 10 i n w t species of ctorrd grain. As regards te~rachlor\innhos. hv also reported tli:~t th15 chem~cnl was morc toxi; than malathion to T. castanhum but less effective against 0. surinamensis and S. granarius. Similar results were obtained in our tests in Cbprus with the exception of T. castaneum which was found equally susceptible to tetrachlorvinphos and malathion. Karein and Kundu Rao (1972), however, reported that the effectiveness of tetrachlorvinphos to S. granarius increased considerably when this chemical was applied as grain treatment at the rate of 8 ppm.

TABLE 1.-COMPARATIVE TOXICITY OF FIVE INSECTICIDES T O VARIOUS STORED GRAIN INSECTS

Concentration ( $ 6 active ingredient)

Insecticide L D C L LD CL Relativet 50 95. 95 95 Potency

Phoxim . . , . 0.048 0.0454.052 0.105 0.0904.123 2.125 Fenitrothion , . 0.016 0.0144.018 0.027 0.0214.034 6.375 Malathion . . . . 0.102 0.093-0.112 0.169 0.136-0.209 1.000 Tetrachlorvinphos . . Not effective Pirimi~hos-methyl . . 0.049 0.047-0.052 0.093 0.085-0.102 2.082

~ i l a t h i o n . . . . 0.059 0.054-0.0 Tetrachlorvinphos . . 0.108 Pirimiphos-methyl . . 0.031

T. cnrtonsurn (CY) Phoxim . . . . 0.026 0.025-0.028 0.055 0.05&0.060 3.846 Fenitrothion . . 0.022 0.0214.023 0.044 0.0394.050 4.545 Malathion . . . . 0.100 0,0924108 0.281 0.2224.356 1.000 Tetrachlorvinphos . . 0.100 0.0864.116 0.369 0,1544.883 1.000 Pirimiohos-methvl . . 0.041 0.039-0.043 0.068 0.0624.074 2.439

0. rurinomenrir (CY) Phoxim . . . . 0.120 0.1094.131 0.566 0.4164.771 0.983 Fenitrothion . . 0.044 0.034-0.056 0.249 0.1424.437 2.682 Malathion . . . . 0.118 0.1094.129 0.472 0.386-0.577 1.000 Tetracnlorvinphos . . 0.541 0.4024.728 7.400 2.680-20.400 0.218 Pirimiphos-methyl . . 0.171 0.1554.189 0.931 0.622-1.390 0.690

T. costmeurn (G.B.)** Phoxim . . . . 0.020 0.018-0.022 0.031 0.0244.040 2.350 Fenitrothion . . 0.018 0.0174.019 0.026 0.0234.029 2.611 Malathion . . . . 0.047 0.0454.050 0.073 0.0684.079 1.000 Tetrachlorvinphos . . 0.042 0.0414.043 0.057 0.054-0.060 1.119 Pirimiphos-methyl . . 0.025 0.0254.026 0.043 0.0384.048 1.880

T. confururn (G.B.) Phoxim . . . . 0.087 0.0814.093 0.139 0.0964.201 1.322 Fenitrothion . . 0.045 0.044-0.046 0.062 0.0584.065 2.556 Malathion . . . . 0.115 0.103-0.129 0.187 0.152-0.230 1.0M) Tetrachlorvinphos . . 0.052 0.0494.054 0.100 0.0854.116 2.212 Pirimiohos-methyl . . 0.078 0.075-0.081 0.122 O.ll(W.135 1.474

CL 95 : 95% confidence limits.

a* (CY), (GB) : Cyprus or English strain.

t The figures of Relative Potency have been worked out for each insect species using LD 50 values and taking that of malathion as one.

Regarding the effectiveness of phoxim McDonald and Gillenwater (1967) reported that this chemical applied topically was more effective than malathion to adults of T. conJusum. Strong (1970) working with the Potter laboratory spray tower also reported that the order of eifectiveliess of test insecticides ag~i t i s t T. confusuri~ was tcti-ochlorvinphos > knitrothion > phoxim > malathion. As regards T. castarzetfm the order of susceptibility was fenitrothion > phoxiin > malathion > tetrachlor\.inpbos. Somewha similar results were obtained in our tests in Cyprus.

Susceptibility of Selected wheat Varieties to the Lesser Grain Borer R. do~ni,,ica. ~-

Of the four wheat varieties included in the first test, Lahish was the most resistant followed by Kyperounda, Pitic 62 and Capeiti 8 which suffered the grcatest pl-ain weight losses. Grain weight loss was proportional to the increase in insect number (Table 2).

T.WLE 2.-SUSCEPTIBILITY O F FOLK WHE-IT VARIETIES EXI'OSED TO 100 ADULTS OF R. DO.WINIC.4 FOR 3 1 , 2 ~IOX'r'llS

Number of rest Insects

i 7 c

i l + b

246-I a

2761 a

Variety

- Lahih . . . . . . . . . . . . Kyperounda.. . . . . . . . . . .

- - -. (a) \leans followed by the same letter do nor difier rign~firindy ar rhc So,, level. Duncan's

niulriple range teat.

The results of a second test with additional wheat varieties are shown in Table 3. The most resistant variety \\'as Tobari 66 folloued by Safed Lrrma and Kyperounda. The rest of the test varieties suffered considerable grain ioeipht losses from R. dontinica attack. The most susceptible variety \ras Hazera ?l52;5101. As i n the prerious test, grain weight loss of each variety was proportional to the increase in number of test insects.

TABU 3.-SUSCEPTIBILITY OF SEI'EX \VHE.kT PARIE'I'JES EXPOSED TO 50 ADULTS OF R. D04111YICrl 1:O11 4 .\IOSl'ITS

Grain a e i ~ h t loss (a)

- 1 9 d

9.0 c

Pitic 62 . . . . . . . . . . 30.6 b

Capeiti 8 . . . . . . . . , . . I . 34.5 a

Variety i Grain a.eipht loas - . . . . Tobari 66 . . . . . . . .

Safed L e m a . . . . . . . . Kyperounda.. . . . . . . . . . . Cspeiti 8 . . . . . . . . . . . .

Mexipak 69 . . . . , . . . . . Blue Silver . . . . . . . . , . . . Huua 2152/5104 . . . . . . . . . .

0

7.3

15.7

28.9

33.3

35.3

67.6

Our findings have shown that contrary to popular belief bread wheat (Aestivum) varieties are not necessarily more susceptible than durum wheat varieties to R. domi- nica attack. Thus the bread wheat varieties Lahish, Tohari, and Safed Lerma suffered smaller weight loss than the durum wheat varieties Kyperounda and Capeiti 8. On the other hand, other bread wheat varietizs like Hazera 215215104, Blue Silver and Mexipak proved very susceptible to R. domb~ica It may be safely argued tliat grain hardness is not primarily responsible for resistance which is probably governed by factors related to the chemical composition of the grain.

Field Trials-I. Effectiveness of Dichlorvos Against Lepidopteroui Pests of Stored Grain.-

( a ) Trikonio trial :-~ Following dichlorvos application in the test store, ail Tree flying adults of P.

interpu~~crclla and S. cert.al~~lla were killed withi11 two hours. Similarly, one hundred percent kill of both species \*as obtained when c a g e containing these pests were placed in the store two hours after treatment.

Two additional dichlorvos applications made at 18-day intervals produced effective reduction in free flying lepidopterous insects.

(b ) Kormakitis trial :- Similarly, satisfactory results were obtained with dichlorvos a t Kormakitis

against lepidopterous pests following daily applications for a period of 40 days. From the catches of sticky traps placed in the store eight days after the initial appli- cation it was evident that a complete control of both P. inrerpunctella and S. cerealella was achieved. Sticky trap catches were taken every week thereafter. The only traps that caught any moths were the two which were placed on top of the grain bulk. In the first week 9 S. cerealella and 2 P. interpunctella adults were caught, whereas 2 P. i~~rrrpu~~ctellu and I S. cerealella were caught in the second week. In the third illid fourth week 2 P. i~~rerpunctella and 2 S. cerealella and 3 P. interpuncrella and 3 S. cerealella were caught respectively.

After the cessation of spray applications, weekly surveys of sticky traps showed that no insects were caught for a period of 4 weeks. However, in the fifth week, two P. inrerpunctella and in the sixth, one S. cerealella were caught.

Satisfactory results were similarly obtained by the use of dichlorvos against lepidoptera and other stored grain insect pests by Green el a / . (1968, 1969). The authors were of the opinion that repeated applications might achieve eradication. La Hue. (1970) and other workers also reported on the effectiveness of dichlorvos vapors against various stored product pests such as Lasioderma serricorne (F) (Tenhet er al. 1957, Childs el a1 1966). Epheslia elutella (Hubner) (Green et a!. 1966). and Anagastn K~rehniellir (Zeller) (Conway 1966). Excellent control was also obtained by Cogburn and Simonaitis (1975) with dichlorvos applied as aerosol against L. serricome, T. custanc~r~?~ and C. caritella in port warehouses.

11. Effectiveness of lodofenphos Wall Treatment Supplemented by Malathion Grain Treatment .- A very satisfactory control of established 7 . granarium infestation was achieved

with an iodofenphos application in the empty store. Sampling of berley coming into storage, showed that it was infested with T. granarium larvae.

- 01 T ~ L E 4.-INSECT SPECIES AND THEIR RELATIVE FREQUENCY PER 203 g O F MALATHION TREATED AND

UNTREATED GRAIN IN AN IODOFENPHOS TREATED STORE

Insect species

Triboliurn spp. . . . .

T. grannrium . . . .

R. dominica . . . .

0. surinamensis . . . . Sitophilus spp. . . . . -

Total . . . .

Grain Moisture content (%)

- Oet.

-

T U T

- 0 6

1 30

I 25

0 4

0 0

- 2 65

-

Aug.

-- T U T

-- 0

1 7 1

0

0

0

-- 1 1 6

--

Sept.

- T U T

5 0 7

7

2 0 5

1 0 I

I 0 0

1 2 0

To : T-fed grain.

UT. : Untreated grain

D a t e o f s a m p l i n g

Nov.

- T UT

-

1 45

0

0

1 82

-

Jan.

- T U T

- 3 1

2 22

1 1

0 0

-

3 26

-

Dec.

- T U T

- 0 2 4 0 1 0 1

0 50

0 1 2 0 2 3 0

I 1 0 0

0 0

- 1 83

--

Feb.

- T U T

- I 1

12 45

0 0

0 0

- 14 47

-

Total

- T U T

- 3 4 6 6

30 414

0 2 7 2

I 1 8

2 2 5

- 39 565

-

Mar. I Apr.

- T U T

- 3 1

5 90

1 0

0 0

0 0 0 1

- 6 93

-

- T U T

-

6 110

0 0

0 0

- 8 116

-

Table 4 summarizes the results of monthly grain samplings taken from both the malathion treated portion of stored barley and the untreated one for a period of ten consecutive months. The commonest insect species were T. granarium followed by Tribolium spp. and R. dominica. Infestation was higher in the untreated portion of grain. The population of T. granarium increased with prolongation of the storage period. Grain moisture content remained low throughout storage with slight increase during the winter months.

111. Effectiveness of Aluminum Phosphide.- Aluminum phosphide applied as Phostoxin (R) tablets at the rate of one tablet/m3

resulted in complete control of a wide range of insect species, including adults of 0. surinarnensis, Tribolium spp., R. dominica, larvae of T. granarium and the grain mite, A. siro infesting bagged barley. At the same time, complete control of four laboratory bred stored grain insects, namely, S. oryzne, R. dominica and T. castaneum adults and T. granarium larvae was achieved after a 72-hour exposure in the treated store.

Phosphine fumigation has been employed for a long time for grain treatment (Monro 1929, Heseltine 1973). Very satisfactory results were also reported by Richardson (1974) against flour beetles and termites in overseas freight containers. Proctor and Ashman (1972) also reported 100 per cent mortality of all stages of T. cnsfaneum, 0. surinamensis and Sitopl~ilus zeamais Motsch when aluminium phosphide pellets were applied to groundnuts in jute or woven polypropylene sacks lined with polyethylene.

IV. Insecticidal Value of Malathion or Bromophos Wall Treatments and Malathion Wall and Grain Treatments Combined, Against Stored Grain Insect Attack.- Table 5 summarizes occurrence records of various stored grain insects developed

in grain in two stores where malathion or bromophos wall treatments were applied one week prior to grain storage.

In the store at Dhali, where bromopbos wall treatment was applied, infestation with T. granarium, S. granarius and T. castaneum increased with the prolongation of the storage period. Infestation with 0. surinamensis and R. dominica remained relatively low during storage. The most serious pests were T. granarium and S granarius.

TABLE 5.-NCIMBER OF INSECTS BY SPECIES PER kg OF GRAIN IN TREATED STORES

Bromophos wall htalathion wall Insect I treatment (Dhali) 1 treatment (Lakatamia)

Date of sampling

S. granarius. . . . . . 0. surinamensis . . T. granarium . . T. castaneum . .

R, dominica . .

Total . . ..

17

3

. . O

. . O

- 5

---I

0

4

0

- 4

11

2

4

- 17

24

3 4 4 5 3

5 1 5 2 4

- 87

8

- 21

46

. . 2 0 0 2 2 6 0 7 4 2 5 1 8

. . 0 0 0 3 2 5 0 0 0 3 2 5 --

34

0

0

0

- 0

-____--- -

4

0

- 12

1 1 1

0

- 16

5

0

1 3

- 13

2

2

3

- 14

19

6

7

- 55

In the store at Lakatamia, where malathion wall treatment was applied, five stored grain insect species were found to infest stored wheat the commonest of which were S. granarius -and 0. surinamensis.

In a third store at Ayia Varvara, which received besides malathion wall treatment an additional malathion dust grain treatment, no living insects were found infesting stored wheat during five months of storage although this store had a history of T. grwariunl infestation in previous years.

The results of this experiment are in agreement with those obtained in tests of previous years (lordanou 1970 b) where malathion or bromophos wall treatments alone failed to provide adequate protection to stored grain during storage, whereas either treatment gave very satisfactory results when it was supplemented with malathion grain treatment. Wall treatments with malathion or bromophos proved very effective in controlling established insect infestations in empty stores prior to grain storage. These treatments however, could not control adequately insects coming into store with the stored grain. Besides, malathion was found to lose its insecticidal action very rapidly when appl~ed on alkaline surfaces such as con- crete, lime, or brick (Parkin 1966, Lemon 1966, 1967, Burckholder and Dicke 1966) contrary to bromophos which is reported to be more stable (Immel and Geisthardt 1964, Kinkel et a / . 1966, Anon 1965). Malathion as grain protectant, however, was reported as an efficient means of control of stored grain insects (Strong et ul. 1961, La Hue 1966, Papwonh 1961). Green and Tyler (1966) also reported that malathion applied at the rate of 10 ppm on stored barley conferred good protection against 0. surinamensis for eight months. Similarly, Spitler and Harstell (1968) found that malathion dust applied at the rate of 6 ppm controlled all stages of 0. mercator and the egg and first instar larvae of P. interpuncfella for 12 months in stored walnuts.

CONCLUSIONS

(a) Grain treatments with malathion, bromopbos, pirimiphos-methyl, tetra- chlorvinphos and fenitrothion were efficient against coleoptera attacking stored grain.

(b) Best results with insect treatments against stored grain coleoptera were obtained by fenitrothion followed by phoxim and pirimiphos-methyl and the poorest results by malathion and tetrachlorvinphos.

(c) Dichlorvos space treatment was efficient against stored grain lepidoptera. (d) Aluminum phosphide fumigation provided excellent control of all insects

attacking stored grain. ( e ) Wall treatment unless supplemented by grain treatment was inadequate

to protect stored grain from insect attack. (f) Resistance to insects was not correlated with grain hardness.

ACKNOWLEDGEMENB

Thanks are due to the Cooperative storekeepers for their valuable assistance. in the implementation of field experiments. The assistance of Mr. C. Hadjiyiannis in field and laboratory work is greatly acknowledged. The author is also indebted to Dr. C. Sergbiou for reviewing the manuscript.

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