THE BIONOMICS OF THE TEAK SKELETONISER, Paliga ...

THE BIONOMICS OF THE TEAK SKELETONISER, Paliga damastesalis

Walker (LEPIDOPTERA: CRAMBIDAE) AND ITS DEFOLIATION IMPACT

ON YOUNG TEAK, Tectona grandis Linnaeus

By

GRACE TABITHA LIM WUI OI

Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in

Fulfilment of the Requirements for the Degree of Master of Agricultural Science

July 2004

2

Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of

the requirements for the degree of Master of Agricultural Science

THE BIONOMICS OF THE TEAK SKELETONISER, Paliga damastesalis

Walker (LEPIDOPTERA: CRAMBIDAE) AND ITS DEFOLIATION IMPACT

ON YOUNG TEAK, Tectona grandis Linnaeus

By


July 2004

Chairman: Professor Yusof Ibrahim, Ph.D.

Faculty: Agriculture

The distribution and feeding behaviour of a teak skeletoniser, Paliga damastesalis

Walker, and the impact of its defoliation on the growth of young teak was investigated

in a series of laboratory and field studies in Malaysia. A laboratory study on feeding

behaviour showed that instar II to V larvae of P. damastesalis significantly preferred

consuming leaf disks cut from young, expanding leaves of nodes 1 to 2 on two year-old

trees, instead of leaf disks cut from mature, fully expanded leaves of nodes 3 to 5. Also,

larvae that were confined to young leaves on pollarded two year-old trees a field study,

fed and developed normally on those whole young leaves, indicating that secondary

metabolites present in young whole leaves do not deter feeding or retard the growth of

this insect significantly. Additionally, in that field study, larvae that were caged over

mature leaves consumed a significantly larger leaf area in the fifth instar and had a

significantly longer larval period than larvae caged over young leaves, while adult dry

weights were not significantly different than that of larvae caged over young leaves.

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This indicates that P. damastesalis may be able to compensate for lower nutritional leaf

content by feeding longer and increasing consumption of the nutrient-poor leaves. The

findings of the laboratory study on the preference of P. damastesalis for younger leaves

were supported by a subsequent study on the within-tree distribution of the immature

stages on 6 to 12 month-old teak planted along a highway. The larvae were strongly

associated with the upper node leaves in the field, which are comparatively younger

than the lower node leaves, suggesting that the larvae preferred and actively sought

younger leaves to consume. However, oviposition behaviour may also have influenced

larval distribution as the larvae may have completed their development on or not far

from the eggs were laid. Since over 60% of the larvae were found on leaves of nodes

two to four, sampling of leaves from these nodes was recommended for young teak

grown in similar conditions, during non-outbreak periods. On another note, a skewed

sex ratio with males consistently forming less than 3.5% of the samples was reported,

and it was suggested that a pathogen causing male mortality in the embrogenic stage of

P. damastesalis may be exerting an influence on those field populations of the insect. In

a ten-month study on the impact of P. damastesalis defoliation on the growth of six

month-old teak in a plantation environment, severity of defoliation showed a significant

negative assocation with production of new leaves and relative growth rates for tree

height and tree collar diameter, only for the first two months after the defoliation. For

the remainder of the study there was no difference in the growth of the trees in relation

to the level of defoliation they experienced.

4

Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai

memenuhi keperluan untuk ijazah Master Sains Pertanian

BIONOMIK ULAT PERANGGAS DAUN JATI, Paliga damastesalis Walker

(LEPIDOPTERA: CRAMBIDAE) DAN IMPAK DEFOLIASI TERHADAP

PERTUMBUHAN POKOK JATI MUDA, Tectona grandis Linnaeus

Oleh


Julai 2004

Pengerusi: Professor Yusof Ibrahim, Ph.D.

Fakulti: Pertanian

Taburan dan tabiat pemakanan ulat peranggas daun jati, Paliga damastesalis Walker

(Lepidoptera: Crambidae), serta impak defoliasi ke atas pertumbuhan pokok jati muda

telah disiasiat dalam kajian bersiri di makmal dan di lapangan di Malaysia. Kajian

pemakanan di makmal menunjukkan bahawa larva P. damastesalis dari instar II-V

memilih makan daun yang dikerat dari daun muda yang masih berkembang iaitu dari

nod-nod 1 hingga 2 pada pokok berumur dua tahun, berbanding daun yang dikerat dari

daun matang yang selesai perkembangannya, iaitu pada nod-nod 3 hingga 5. Juga, larva

yang disangkarkan pada daun muda pokok yang dicantas yang berumur dua tahun di

lapangan didapati makan dan berkembang secara biasa, menunjukkan bahawa metabolit

sekunder dalam daun muda pokok lapangan tidak menghindar pemakanan atau

merencatkan perkembangan serangga ini. Kajian tersebut juga mendapati bahawa larva

yang disangkarkan pada daun matang telah memakan kawasan daun yang lebih luas

semasa instar V dan tempoh peringkat larva lebih panjang berbanding larva yang

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disangkarkan pada daun muda, tetapi berat kering dewasanya tidak berbeza. Maka P.

damastesalis mungkin mengubahsuai pemakanannya dalam keadaan diet yang rendah

tahap nutrien dengan meningkatkan kuantiti pemakanan dan melanjutkan tempoh

pemakanannya. Pemilihan daun muda oleh P. damastesalis yang ditunjukkan di

makmal telah disokong oleh kajian seterusnya di lapangan terhadap taburan peringkat

muda serangga ini pada pokok yang berumur 6 hingga 12 bulan yang ditanam di

sepanjang jalanraya. Larva ditemui pada daun di nod-nod bahagian atas pokok, yang

lebih muda berbanding daun di nod-nod bahagian bawah. Ini mungkin disebabkan

pergerakan larva ke daun-daun muda tersebut yang merupakan makanan pilihan

mereka, tetapi mungkin juga disebabkan oleh tabiat peneluran betina dewasa di mana

perkembangan larva disempurnakan pada atau berhampiran tapak peneluran. Oleh

kerana lebih daripada 60% larva didapati pada daun di nod-nod 2 hingga 4,

pengsampelan daun nod-nod tersebut disarankan untuk pokok jati muda yang ditanam

dalam keadaan sepertimana dalam kajian tersebut, dan di luar masa wabak. Nisbah seks

yang tidak seimbang telah ditemui di mana komposisi serangga jantan didapati kurang

dari 3.5% daripada sampel-sampel. Sejenis kuman penyebab mortaliti pada peringkat

embrio P. damastesalis mungkin menghadkan populasi serangga di kawasan tersebut.

Dalam kajian impak defoliasi pada pokok jati berumur enam bulan di sebuah hutan

ladang, tahap defoliasi dihubungkaitkan dengan pengurangan signifikan kadar

pertumbuhan pokok jati berumur enam bulan hanya dalam dua bulan pertama selepas

defoliasi tersebut, dan di sepanjang tempoh kajian selepas itu, tahap defoliasi yang

dialami sesuatu pokok didapati tidak memberi kesan terhadap kadar pertumbuhan

pokok tersebut.

6

ACKNOWLEDGEMENTS

I am greatly indebted to Prof Dr Yusof Ibrahim (UPM) for his constant encouragement

and constructive criticism particularly during the challenging and difficult period of

thesis writing. It was a privilege to have been able to study under him, and our

discussions never failed to uplift my spirits, build confidence, and fuel my zeal to

redouble efforts in bringing this present work to completion. Thanks also to Dr Faizah

Abood Harris (UPM) for her constructive criticism on the manuscript and invaluable

suggestions that helped improve it. I wish to thank Dr Gary Theseira (Ecophysiology

Unit, FRIM) and Ms Emily Heffernan (University of Florida) who provided critical

reviews of various chapters.

I would also like to put on record my heartfelt gratitude towards the Chairperson and

members of my examination committee: Assoc Prof Dr Rohani Ibrahim, Prof Dr

Ahmad Said Sajap and Prof Dr Dzolkifli Omar (UPM), and Dr Mohamad Basri Wahid

(MPOB), for their criticism of my thesis that significantly improved it.

My deepest thanks goes to Dr Laurence G. Kirton (Entomology Unit, FRIM). His

supervision of my project went beyond the call of duty. The countless hours he spent

working with me was a priceless study in good research methods and conscientious

reporting that has shaped my values and principles as a researcher. He is my colleague,

mentor, and friend.

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I am very grateful to Dr Khoo Khay Chong (UPM, retired Professor) not only for his

supervision of my project, but also for being my mentor. He was the person who first

inspired my interest in insects as an undergraduate student, guided me through my first

degree, and my present project. He is the person to whom I say a silent ‘thank you’

every time I think of the fulfilment and happiness entomological research brings me.

I would like to express my warmest appreciation to Ms Saimas Ariffin (Entomology

Unit, FRIM) for her assistance in the project and her keen observations and ideas that

helped refine the experiments. Thanks also to En Azmi Mahyudin, En Saiful Azahari,

En Shaiful Amri, Pn Norziah Ishak, Pn Rohayu Yunus and En Rosle Abd Rahman

(Entomology Unit, UPM). I am very grateful to Dr Hashim Md Nor (FRIM Mata Ayer

Field Station, Perlis) for his kind assistance in my field studies, and to the staff of Mata

Ayer Field Station. Immense thanks goes to Dr Baskaran Krishnapillay (Biotechnology

Division, FRIM) for his big-heartedness in always making time for me. His friendly

encouragement and advice meant so much to me as a young researcher in FRIM.

Last but not least, I would like to express my appreciation and love to God, my family,

my beloved and my dear friends. You saw me through the darkest and most trying

period of my life. I would not have pulled through, much less finished this thesis,

without your love, support and care.

The research was supported by IRPA 30070102001 “Developing integrated pest

management strategies for teak in Malaysia” (1999-2001).

8

I certify that an Examination Committee met on 23rd

July 2004 to conduct the final

examination of Grace Tabitha Lim Wui Oi on her Master of Agricultural Science thesis

entitled “The Bionomics of the Teak Skeletoniser, Paliga damastesalis Walker

(Lepidoptera: Crambidae) and Its Defoliation Impact on Young Teak, Tectona grandis

Linnaeus” in accordance with Universiti Putra Malaysia (Higher Degree) Act 1980 and

Universiti Putra Malaysia (Higher Degree) Regulations 1981. The Committee

recommends that the candidate be awarded the relevant degree. Members of the

Examination Committee are as follows:

ROHANI IBRAHIM, Ph.D.

Associate Professor

Faculty of Agriculture

Universiti Putra Malaysia

(Chairman)

AHMAD SAID SAJAP, Ph.D.

Professor

Faculty of Forestry


(Member)

DZOLKIFLI OMAR, Ph.D.

Professor



(Member)

MOHD. BASRI WAHID, Ph.D.

Deputy Director General

Malaysian Palm Oil Board

(Independent examiner)

__________________________________

GULAM RUSUL RAHMAT ALI, Ph.D.

Professor/Deputy Dean

School of Graduate Studies,


Date:

9

This thesis submitted to the Senate of Universiti Putra Malaysia and has been accepted

as fulfilment of the requirement for the degree of Master of Agricultural Science. The

members of the Supervisory Committee are as follows:

YUSOF IBRAHIM, Ph.D.

Professor



(Chairman)

FAIZAH ABOOD HARRIS, Ph.D.

Faculty of Forestry


(Member)

LAURENCE G. KIRTON, Ph.D.

Entomology Unit

Forest Research Institute Malaysia

(Member)

_________________________

AINI IDERIS, Ph.D.

Professor/Dean

School of Graduate Studies


Date:

10

DECLARATION

I hereby declare that the thesis is based on my original work except for quotations and

citations which have been duly acknowledged. I also declare that it has not been

previously or concurrently submitted for any other degree at UPM or other institutions.

________________________________


Date:

11

TABLE OF CONTENTS

Page

ABSTRACT 2

ABSTRAK 4

ACKNOWLEDGEMENTS 6

APPROVAL 8

DECLARATION 10

LIST OF TABLES 13

LIST OF FIGURES

15

CHAPTER

1 INTRODUCTION

17

2 LITERATURE REVIEW 21

Distribution and Economic Importance of Paliga damastesalis Walker 21

The Host Plant: Tectona grandis Linnaeus (Verbenaceae) 23

The Life History of P. damastesalis 26

Management of P. damastesalis

29

3 GENERAL METHODOLOGY 33

Study Sites 33

Test Insects

35

4 THE FEEDING PREFERENCE, FEEDING BEHAVIOUR AND

GROWTH PERFORMANCE OF Paliga damastesalis Walker IN

LABORATORY AND FIELD CONDITIONS

36

Introduction 36

Materials and Methods 38

Results 47

Discussion

50

5 THE DISTRIBUTION OF Paliga damastesalis Walker ON YOUNG

TEAK IN THE FIELD

54

Introduction 54


Results 59

Discussion

71

6 THE EFFECT OF DEFOLIATION BY Paliga damastesalis Walker

ON THE GROWTH OF YOUNG TEAK IN THE FIELD

79

Introduction 79


Results 85

Discussion 100

12

7 GENERAL DISCUSSION AND CONCLUSION

108

REFERENCES 113

APPENDICES 121

BIODATA OF THE AUTHOR 135

13

LIST OF TABLES

Table Page

4.1. Mean leaf area consumed (cm2 ± S.D.) by P. damastesalis larvae (instars

I-V) provided both young and old leaf disks in the laboratory choice test

47

4.2. Feeding and development of P. damastesalis larvae (instars I-V) in the

no-choice field test, showing mean leaf area consumed (cm2 ± S.D.),

larval duration (days ± S.D.) and adult dry weight (mg ± S.D.).

49

4.3. The measurements of body length (mm ± S.D.) of P. damastesalis larvae

at different stages of development and the duration (days, 95%

confidence) of each stage (Appendix 4.1)

121

4.4. Determination of larval instars by examining daily leaf area consumption

patterns of P. damastesalis larvae that were caged over young and old

leaves in the laboratory choice test (cm2) (Appendix 4.2)

122

4.5. Leaf area consumed by P. damastesalis larvae (instars I-V) provided with

both young and old leaf disks in the laboratory choice test (cm2)

(Appendix 4.3)

123

4.6. Determination of larval instars by examining daily leaf area consumption

patterns of P. damastesalis larvae that were caged on young or old leaves

in the field study (cm2) (Appendix 4.4)

124

4.7 Leaf area consumed (cm2), larval duration (days) and adult dry weight

(mg) of P. damastesalis larvae (instar I-V) that were caged on young or

old leaves in the field (Appendix 4.5)

125

5.1. Site localities and characteristics for the two assessments conducted along

the North-South Highway, Malaysia

57

5.2. Data recorded on the location and developmental stage of each occurrence

of P. damastesalis on trees at the study sites

58

5.3. Density of P. damastesalis (mean number of insects per 100 nodes ±

S.D.) in relation to leaf age as indicated by node number for site A

62

5.4. Density of P. damastesalis (mean number of insects per 100 nodes ±

S.D.) in relation to leaf age as indicated by node number for site B

62

5.5. Distribution of immature stages on leaves facing different bearings at site

A

69

14

5.6. Distribution of P. damastesalis on leaves facing different bearings in

relation to leaf aspect at site A.

69

5.7. Numbers of each developmental stage of P. damastesalis occurring on the

upper and lower leaf surfaces in site A and site B (Appendix 5.1)

126

5.8. Chi-Square test for numbers of the various immature stages occurring at

the two study sites (Appendix 5.2)

127

5.9. Chi-Square test for numbers of insects occurring on the upper and lower

leaf surfaces of leaves facing different bearings at site A (Appendix 5.3)

128

5.10 Chi-Square test for numbers of the various immature stages occurring at

the two study sites (Appendix 5.4)

129

6.1 Defoliated area (%) for each level of leaf defoliation

82

6.2 Overall tree defoliation (%) for each defoliation class

83

6.3 Correlation matrix showing associations and interactions between

defoliation, initial tree height and collar diameter, and RGRH, RGRC and

production of new leaves over time

90

6.4 Defoliation level in relation to RGRC, RGRH, and new leaf production up

to nine months after the outbreak

95

6.5 Chi-Square test for numbers of trees that were damaged and undamaged

by the end of the study, in relation to the defoliation severity experienced

at the start of the study (Appendix 6.3)

132

6.6 General Linear Model ANOVA with multiple comparisons between the

factors of defoliation, tree height class and their interaction, in relation to

overall RGRH for the entire study duration (nine months) (Appendix 6.4)

133

15

LIST OF FIGURES

Figure

Page

1.1 Various stages of the life cycle of the teak skeletoniser, P. damastesalis

27

4.1. Relationship between the number of cells on the surface of a teak leaf

portion and the leaf portion area (cm2)

40

4.2 Clip cage designed to confine a larva of P. damastesalis to a teak leaf

44

4.3 Leaf area consumed by a P. damastesalis first instar during a 24 hr period

with 1cm2 graph paper as the reference

45

5.1. Ordination of leaf node position, leaf aspect and stage of development at

Site A, by correspondence analysis (n = 221)

60

5.2. Ordination of leaf node position, leaf aspect and stage of development at

Site B, by correspondence analysis (n = 144)

61

5.3. Density of P. damastesalis (mean number of insects per 100 nodes ± S.D.)

in relation to leaf age as indicated by node number at both study sites

64

5.4. Percentage of P. damastesalis on upper and lower leaf surfaces at site A and

site B

66

5.5. Ordination of leaf bearing and stage of development at Site A, by

correspondence analysis (n = 221)

68

5.6. Abundance of the different developmental stages of P. damastesalis at the

two study sites

70

6.1. Percentage of trees that were dead or bent/snapped by the end of the study in

December, in relation to the severity of defoliation experienced at the start

of the study in March

86

6.2. Patterns of interactions for mean new leaf production, RGRC and RGRH

(month-1

± S.E.), over time, in relation to rainfall (mm), after the outbreak of

P. damastesalis (n=436)

88

6.3. Initial height of trees in relation to the level to which they were defoliated

(a), RGRH of the trees a month after the outbreak in relation to their

defoliation level (b), their initial height (c) (n = 436)

91

16

6.4. Initial collar diameter of trees in relation to the level to which they were

defoliated (a), RGRC of the trees a month after the outbreak in relation to

their defoliation level (b), and their initial collar diameter (c) (n = 436)

92

6.5. Production of new leaves a month after the outbreak in relation to initial

collar diameter (a), initial height (b), and level of defoliation (c) (n = 436)

96

6.6. The partial correlation between defoliation level and RGRH (a), RGRC (b),

and new leaf production (c), one month after the outbreak, with initial tree

height, initial collar diameter and initial tree height respectively, held

constant (n = 436)

97

6.7. Relationship between defoliation level and mean RGRH (month-1

± S.E.)

over nine months, in relation to the height class of the trees at the time of the

outbreak

99

6.8 Examples of four levels of defoliation on a teak leaf (Appendix 6.1)

130

6.9. Tree coordinates showing trees that were damaged and dead by the end of

the study in December, and the undamaged trees (n = 436) with their

respective defoliation levels. (Appendix 6.2)

131

17

CHAPTER 1

INTRODUCTION

Paliga damastesalis Walker is a serious pest of young teak (Tectona grandis Linnaeus)

in Peninsular Malaysia (Intachat et al., 2000a) and the most important pest of teak in

Sabah (Chey, 1999). It is one of the two economically important teak skeletoniser

species in the world, the other being Paliga machoeralis Walker (syn: Eutectona

machoeralis, Hapalia machaeralis, Pyrausta machaeralis (Roychoudhury & Joshi,

1997)), a closely related species of P. damastesalis that is a major pest of teak

plantations in India (Patil & Thontadarya, 1983b; Mishra, 1992). It can cause up to a

100% defoliation of teak during outbreaks (Intachat, 1999), and is the chief cause of

concern to the expanding plantation sector, which places much importance of teak as a

valuable timber species (Baskaran et al., 1998). Teak is an exotic timber species in

Malaysia, being indigenous to India, Myanmar, Thailand, Laos, Cambodia and

Vietnam.

As teak is an important export and a forest plantation species in India, the teak

skeletoniser species occuring there, i.e., P. machoeralis, has been researched

extensively for many years. Numerous studies on its life history, behaviour, ecology,

population dynamics and various control methods have been conducted (e.g., Misra,

1975; Patil & Thontadarya, 1983a; Patil & Thontadarya, 1987; Meshram, 1995;

Meshram et al., 1997; Roychoudhury, 1999). While there is a great deal of information

18

available on P. machoeralis, only basic research has been conducted on P.

damastesalis, following the recent emphasis on planting teak in Malaysia. Local

research has yielded information on the life history of P. damastesalis (Intachat, 1999)

and established that it is a different species from P. machoeralis, although similarities

exist between the two (Intachat, 1998). Aqueous and methanol extracts of sentang leaf,

bark and wood (Azadirachta excelsa) were found to suppress feeding of P.

damastesalis, and some isolates of the microbial insecticide Bt (Bacillus thuringiensis,

vars. kurstaki and aizawai) have been reported to have potential as environmentally-

friendly insecticides for controlling this insect pest (Ng et al., 1998; Intachat et al.,

2000c). Bt is a microbial insecticide used for control of a number of lepidopteran,

dipteran and coleopteran pests by way of ingestion of the endotoxin it produces and

subsequent paralysis of the insect gut (Schnepf et al., 1998) , while sentang is one of the

two important congeneric species of neem (Azadirachta indica), of which leaf and seed

extracts are used in commercial biopesticide formulations (Ng et al., 1999).

Paliga damastesalis has a life cycle of only 38 days and the female is capable of laying

more than 100 eggs on average. The larvae feed on the succulent lamina and avoid the

leaf veins and ribs, thus leaving the skeletonised leaf characteristic of defoliation caused

by P. damastesalis (Intachat, 1999). Defoliation by the teak skeletoniser in Thailand,

India, and Bangladesh has been shown to retard growth of the trees (Kirtibutr, 1983;

Nair et al., 1996; and Baksha & Crawley, 1998a), and it is conjectured that defoliation

on teak by P. damastesalis would similarly affect the trees (Intachat, 1997). However,

not much is known concerning the actual impact of defoliation by P. damastesalis on

19

teak trees grown locally. Knowing the extent to which defoliation may affect the growth

rate of the trees is important in deciding when to intervene with appropriate pest control

methods in order to prevent serious losses in growth.

The study on the life history of P. damastesalis elucidated the duration and size of the

five larval instars of the insect and included some observations on feeding behaviour

(Intachat, 1999), but much more remains to be explored in the aspect of feeding

behaviour, such as preference and factors influencing preference, if any. It was found

that the fourth instar larvae of P. machoeralis that were fed young teak leaves gained

more weight than those given mature leaves (Roychoudhury et al., 1995). This

however, was a no-choice experiment, and while it observed that P. machoeralis

preferred young leaves (Roychoudhury & Joshi, 1997), it was not quantified.

Outbreaks were observed to be seasonal (Tewari, 1992), and in Bangladesh it coincided

with new flush of leaves (Baksha & Crawley, 1998b). Likewise, outbreaks of P.

damastesalis in Malaysia are observed to be seasonal, but observations differ. Intachat

et al. (2000b) noted attacks in Sabah were more severe during the dry spells, while

Chey (1999) believed that the pest was more abundant during wetter periods. In Perlis,

it was observed that defoliation coincided with the flushing of leaves following the

onset of the southwest monsoon in March (Tho, 1981). Thus there is a need to

investigate the possible seasonal abundance of this pest through regular monitoring of

field populations. Currently, no sampling method has been recommended for estimating

field populations of the teak skeletoniser, and for monitoring its population dynamics.

20

For the successful management of this pest, a thorough understanding of its behaviour

and the factors which influence its distribution is essential. Towards this end, a series of

studies was conducted with the following objectives:

First, to investigate the feeding behaviour of P. damastesalis under laboratory and field

conditions. The laboratory study aimed to determine larval preference with regard to

leaf age. To complement the laboratory study, the field study was designed to provide a

comparison of leaf consumption and development between larvae fed excised leaves in

the laboratory and larvae caged over leaves on trees in the field, in the context of

secondary metabolite differences between the two. Additionally, the field study aimed

to assess the influence of leaf age on leaf consumption and larval development.

Second, to determine the within-tree distribution of P. damastesalis on trees in the field.

This study would provide the initial results that could be used as a basis for future

development of a reliable sampling method for the pest. The findings of this study

regarding the influence of larval food preference on the distribution of the larvae among

the leaf nodes within each tree would complement results from the previous studies on

feeding behaviour in the laboratory and field

Third, to measure the impact of defoliation by P. damastesalis on teak. The effects of

defoliation on the growth increment of young teak trees were investigated and

quantified in order to provide reasonable justification for further research on the insect.

21

CHAPTER 2

LITERATURE REVIEW

Distribution and Economic Importance of P. damastesalis Walker

The teak skeletoniser, Paliga damastesalis Walker, is found in Malaysia and Java. It has

accompanied the introduction of teak (Tectona grandis Linnaeus) as an exotic species

grown in forest plantations. In India, Myanmar, Thailand, Laos, Cambodia and

Vietnam, where teak is indigenous (Appanah & Weinland, 1993), the teak skeletoniser

is an important pest of teak. However, in India and Myanmar, the teak skeletoniser is

Paliga machoeralis Walker (syn. Eutectona machoeralis Walker, Hapalia machaeralis

Walker, Pyrausta machaeralis Walker (Roychoudhury & Joshi, 1997)), and while

likewise identified in Thailand, more recent work has suggested the possibility that the

teak skeletoniser species in Thailand is also P. damastesalis (Intachat, 1998). The two

species are very similar and Eutectona is regarded as a junior synonym of Paliga

(Shaffer et al., 1996). E. machoeralis is also referred to in literature as Pyrausta

machoeralis, but it may be more accurate to refer to these as Paliga machoeralis

(Intachat, 1998). In both damastesalis and machoeralis, the wings are yellow, but while

damastesalis has red markings on the forewings, machoeralis has grey markings on

both fore- and hind wings.

22

In India, Bangladesh and Thailand, P. machoeralis ranks together with another

defoliating insect, Hyblaea puera Cramer, as a major pest of teak. As teak is an

important export and a forest plantation species in these countries, teak skeletoniser

species has been researched intensively for many years. In Malaysia P. damastesalis has

also established itself as a serious pest, where outbreaks result in heavy teak defoliation

(Tho, 1981; Chey, 1999). The trees are known to have been completely defoliated in

some instances (Intachat, 1999). The recent emphasis on planting teak in Malaysia has

stimulated research efforts on this teak skeletoniser species. This is timely in view of

the government’s efforts to intensify research in the priority areas of integrated pest

management and sustainable forest management in plantation forests, particularly for

lucrative timber species such as teak (Baskaran, 2000).

In Malaysia, although the trees rarely die even when completely defoliated, growth may

be depressed, and the forking that often occurs young teak trees after severe defoliation

results in future economic losses (Intachat, 1997). In Bangladesh, growth increment of

teak trees has been shown to be greatly reduced by artificial defoliation. Yearly

defoliation of 50% for four consecutive years on one year-old teak, caused serious

losses in height, basal area and volume increment of 36, 55 and 62% respectively

(Baksha & Crawley, 1998a). Reported losses in volume increment attributed to P.

machoeralis defoliation varied from 8.3% to 65% following three periods of heavy

defoliation in one growing season (reviewed by Tewari, 1992). In Thailand, there was a

48% reduction in radial growth after three consecutive artificial defoliations of 25%

conducted in one growing season (Kirtibutr, 1983). Meanwhile, although the

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defoliation levels by P. machoeralis in India did not significantly affect the growth of a

four year-old teak stand in a five year study, complete defoliation by the teak leaf roller,

H. puera, caused a 44% loss in potential increment (Nair et al., 1996).

It is likely that the impact of defoliation on locally grown teak would be equally

adverse, and it would be useful to evaluate the impact of such loss of leaf area on

growth. In addition to affecting growth, insect defoliation on plants directly and/or

indirectly affects plant vigour, performance, competitiveness, recruitment, demography,

and fitness. Furthermore, how the plant responds to a defoliation event depends on its

type and age, species characteristics, available resources and the ecological context

(Nowierski et al., 1999). In Malaysia, with the exception of an artificial defoliation

experiment on seedlings in a potted trial (Hashim, 2003), the effect of defoliation on

teak trees has not been studied. This has resulted in differing recommendations as to the

levels of defoliation that warrant application of control measures, e.g. 30 to 50% (Tho,

1981), and exceeding 50% (Intachat, 1997). Much more information on the effect of P.

damastesalis defoliation on teak is needed to evaluate its impact on growth

performance, and for the formulation of economic injury levels and effective

management strategies so that timely control measures can be applied.

The Host Plant: Tectona grandis Linnaeus (Verbenaceae)

Teak is a large tree, growing up to 45 m in height and attaining diameters of up to 100

cm. It is deciduous in nature and sheds it leaves during the dry season, which in

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Malaysia is from the end of December to March, depending on soil moisture and

varying with locality, while dormant buds emerge after the April to May rainy season

(Hashim & Mohd Noor, 2002). Site requirements include deep, well-drained calcareous

soil, with a neutral pH and annual rainfall of between 900 and 1600 mm (Behaghel,

1999). The root system of teak is superficial and depending on soil conditions, the

feeding roots penetrate to a depth of 70 to 80 cm (Hashim & Mohd Noor, 2002).

Additionally, a well-defined dry season is preferable, and in Peninsular Malaysia, teak

thrives in the northern states that have a more pronounced dry spell, although growth

performance further south has also been good. Under optimum conditions, one meter

height increment a year can be achieved (Baskaran et al., 1998). A survey in Mata

Ayer, Perlis, showed that the mean annual diameter growth of teak ranged from 1.1 to

1.5 cm for stands aged 8 to 31 years of age (Tang & Abd Kadir, 1979) and the MAI for

volume has been estimated to be 5.0 to 6.0 m3y

-1 (Sandrasegaran, 1972).

The bark of teak is fibrous with shallow longitudinal cracks, and on older trees it peels

off in long, thin narrow flakes. It is greyish brown in color and up to 15 mm thick, while

inner bark is yellowish in color. Teak leaves are large, elliptic or obovate and entire, and

are between 25 to 50 cm long and between 15 to 35 cm wide. Juvenile leaves are larger

in size. The leaves are opposite on the stems. The upper sides of the leaves vary from

rough to smooth and range from light to dark green in color, while the under sides are

velvety and covered with tomentum (hairs) that range from grey, whitish to tawny in

coloration. Young shoots vary from reddish green to brownish in color (Hashim &

Mohd Noor, 2002).

THE BIONOMICS OF THE TEAK SKELETONISER, Paliga ...

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