Development and implementation of IPM 249

Dynamism in diamondback moth IPM development:The Malaysian experience

Loke, W. H., Syed Abd. Rahman, Sivapragasam, A., Fauziah, I.,Md. Jusoh, M. and Hussan, A.K.

MARDI, P.O. Box 12301, G.P.O. 50774 Kuala Lumpur

AbstractThe development of an IPM program for diamondback moth (DBM) in Malaysia comprised severaldistinct stages. These ranged from initial appraisal of the problem and examination of strategic options,to component identification, development and integration, and eventual evaluation of interim IPMpackages.

The initial IPM packages developed in the 70s and early 80s consisted of need-based treatmentswhen tentative economic threshold levels (ETL) were exceeded. Several ETLs were evaluated. Over theyears, as additional information became available, the initial IPM packages were refined and improved.Basically, this involved modifying the adopted thresholds and incorporating the role of parasitoids in theETL. In 1987, the thresholds were again modified, respectively, to 4 larvae/plant and 7 larvae/plant withparasitism rate of at least 40% as a sub-parameter (IPM I).

Over the last few years, two variant packages (IPM II and IPM III) which take into considerationcrop phenology have been developed and evaluated. Essentially, these packages were based on the rationalethat the early phase of the cabbage crop (pre-heading) was more susceptible to economic damage byDBM than the later phase and needed more protection. A total of 5 trials in 2 locations (Cameron Highlands– 3, Jalan Kebun – 2) were conducted to compare all three IPM packages. Results showed that IPM IIwas the most superior package of the three in terms of yield and net profits. It is also the package withthe least stringent ETLs, which further reduces the pressure to spray.

In addition to refinement of the DBM IPM package based on crop phenology, improvement throughthe use of a composite Plutella Equivalent threshold was also developed. This makes the IPM packagemore holistic as other major pests such as Hellula, Spodoptera and Phyllotreta are also addressed in thedecision-making process.

Besides the utilisation/encouragement of classical biological control, other biologically-basedtechnologies such as beneficial plants, trap crop, bioactive compounds (pheromones), botanical pesticidesand F1 sterility have also been studied and considered as potential tactics for the improvement of DBMIPM.

Key words: Diamondback moth, IPM, biologically-based technologies, Malaysia

IntroductionPlutella xylostella (L.) (Lepidoptera; Yponomeutidae),the diamondback moth (DBM), was first recorded inMalaysia in 1925. By 1941, it had become widelyestablished all over Malaysia as a serious pest ofcrucifers. To-date, DBM remains as the mostwidespread and important pest of brassicas in Malaysia(Loke et al., 1992a).

Since the 1940s, pesticides have been the mainmethod of control practised by farmers. The demandfor these synthetic chemicals has been substantial andseems endless. Such overdependence on insecticideshas led to several pesticide-related problems such asresistance development, hazards to non-targetorganisms (NTOs), environmental pollution, poisoningand residues in the harvested produce.

In the 1970s, an ecological approach was adoptedto manage the DBM problem. Research was intensifiedin biology, ecology and control tactics, particularlybiological control and/or biologically-basedtechnologies (BBTs), to develop a more sustainableand eco-rational approach to manage the DBM

problem. This paper traces the dynamic developmentof integrated pest management (IPM) of DBM inMalaysia over the years.

Development of DBM IPM and initial packagesThe development of DBM IPM in Malaysiaencompassed several distinct stages. These stagesinvolved initial appraisal of the problem, examinationof strategic options, component identification, furtherdevelopment of component tactics, integration andeventual evaluation of the IPM package at farm level.

Several options were investigated, includingresistant varieties, cultural management techniques,novel approaches like hormonal control and use ofantifeedants. However, these approaches were foundto be largely exploratory in nature, and mainlyconfined to laboratory situations (Loke et al., 1992a;Syed, 1992). Success in the suppression of DBM withthe use of biological control has been reportedelsewhere (Loke et al., 1992a). The biological controlapproach, therefore, was given priority considerationin the DBM-IPM model.

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With the acceptance that natural enemies orparasitoids (Cotesia plutellae, Diadegma semiclausum,Diadromus collaris) can play a significant role,attempts were then made to begin formulating an IPMprogramme for DBM that encourages or enhances theaction of this core component. The initial IPMapproach, in contrast with the farmers’ regime offrequent and heavy doses of insecticides, consistedessentially of need-based treatment when the tentativeeconomic threshold level (ETL) of five larvae per tenplants was exceeded. Bacillus thuringiensis (Bt) wasapplied beyond this ETL. Synthetic insecticides wereonly used when infestation increased to 37 larvae perten plants. In this first IPM programme, the impact ofnatural enemies was not incorporated in decision-making with regard to application of insecticides,largely because of inadequate ecological data then.From the first six trials conducted in both farmers’fields and experimental plots, it was found that severalof the cabbage crops managed with the IPM approachwere marginally superior in terms of economic returnsas compared to farmers’ fields (Sivapragasam et al.,1985).

Over the years, as additional information becameavailable, the original IPM programme was modified.The modifications concerned improving decision-making with respect to action needed on treatment.Essentially, these involved refining and improving theadopted thresholds as well as incorporating the roleof parasitoids. For example, initial ETLs of five larvaeper ten plants and 37 larvae per ten plants were, inlater trials, changed to 15 and 37. These still did notincorporate the contribution of biological controlagents. Subsequently, a further change was madewhereby irrespective of the infestation level of DBM,no insecticide was allowed when the DBM larvae hadat least 40% parasitization level.

In 1987, the ETLs were again modified. This IPMpackage, viz. IPM I, consisted of a three-tiered ETLwhich takes in account the percentage parasitizationof the DBM larvae (Table 1). Results of trials in thehighlands and the lowlands clearly established thesuperiority of IPM I over prophylactic control practisedby cabbage farmers (Table 2 and 3). Marketable yieldswere 5–60% higher and up to 6-fold increases in profitswere obtained in the IPM plots. The number ofinsecticide applications was also significantly reducedfrom 7 to 9 times in prophylactic plots to a maximumof only three applications in IPM plots (Syed et al.,1992).

The series of IPM trials conducted between 1987–91 showed that, in general, IPM can provide highernet revenue when compared to farmers’ practice ofusing insecticides prophylactically without any regardfor natural enemies. IPM also required fewer sprays,and yet was able to secure marketable heads. Noinsecticide residue was detected in the crops harvestedfrom IPM plots.

The IPM development studies carried out so farhave also shown that IPM was both promising andhighly encouraging. Even without considering the

Table 1. IPM I package for DBM Malaysia

Crop age Economic Threshold DecisionLevel (ETL)

Week 1–10 <4 DBM larvae/plant No spray>4 <7, parasitisation >40% No spray>4 <7, parasitisation <40% Spray Bt>7 Spray

synthetics

intangibles, such as reduced environmental pollution,less upset of existing natural balance and sustainedecological stability, etc., the decline in insecticidalinputs alone is sufficient to favour IPM over theexisting over-indulgent chemical approach of farmers.Clearly, over the long term, the ecological benefits arelikely to prove highly significant.

Further IPM refinement and consideration of otherbiological tacticsOver the last few years, further work to refine IPM Iwas carried out. This resulted in the development andtesting of two variant packages, viz. IPM II and IPMIII, which take into consideration crop phenology.Essentially, these two packages were based on therationale that the early phase of the cabbage crop (pre-heading) was more susceptible to economic damageby DBM as compared to the later phase. Thus, theearlier phase needed more protection and the ETLduring this phase should be more stringent as comparedto that for the later phase. Details of IPM II and IPMIII are shown in Table 4. A total of five trials in twolocations involving cabbage crops (CameronHighlands – 3 crops; Jalan Kebun – 2 crops) wereconducted to compare the performance of the threeIPM packages. Results showed that IPM II was themost superior of the three packages in terms of yieldand net profits. Table 5 shows the results for thehighland trials. IPM II is also the package with theleast stringent ETLs. This means that the need orpressure to conduct spraying is further reduced, which

Table 3. Summary of IPM I trials in Jalan Kebun, Kelang(Lowlands)*

IPM Prophylactic

Cabbage yield (tonnes/ha) 17.7 9.20Gross returns @ RM0.80/kg 14 160 7 360Production costs (RM/ha) 8 345 8 925Nett returns (RM/ha) 5 815 (1 565)Sprays frequency (min.–max.) 1–3 7–9

*Mean of 3 trials conducted between 1989–1991 (on peatsoil)

Table 2. Summary of IPM I trials in Cameron Highlands*

IPM Prophylactic

Cabbage yield (tonnes/ha) 29.1 26.2Gross returns @ RM0.80/kg 23 280 20 987Production costs (RM/ha) 8 966 9 427Nett returns (RM/ha) 14 314 11 560Sprays frequency (min.–max.) 0–1 7–9

* Mean of 3 trials conducted between 1989–1991.

Development and implementation of IPM 251

Table 4. IPM II and IPM III packages for DBM in Malaysia

Crop age Economic Threshold Level (ETL) Decision

A. IPM IIWeek 1–4 <4 DBM larvae/plant No spray

>4 <7, parasitization >40% No spray>4 <7, parasitization <40% Spray Bt>7 Spray synthetics

Week 5–10 <8 DBM larvae/plant No spray>8 <14, parasitization >40% No spray>8 <14, parasitization <40% Spray Bt>14 Spray synthetics

B. IPM IIIWeek 1–4 <2 DBM larvae/plant No spray

>2 <4, parasitization >40% No spray>2 <4, parasitization <40% Spray Bt>4 Spray synthetics

Week 5–10 <4 DBM larvae/plant No spray>4 <7, parasitization >40% No spray>4 <7, parasitization <40% Spray Bt>7 Spray synthetics

Table 5. Comparison of three IPM packages to controlDBM in Cameron Highlands, Malaysia (mean of 2 trials)

IPM I IPM II IPM III

Total yield/plot (kg) 1 146 1 189 1 062Profits (RM) 762 782 634

grammatoidea bactrae fumata and Oomyzussokolowski. This core group of biological controlagents together with other potential ones like nuclearpolyhedrosis viruses (NPV), the entomopathogenicfungus, Erynia radicans and entomopathogenicnematodes Steinernema spp. constitute the classicalbiological control approach, which has been the corecomponent tactic in the DBM IPM programme inMalaysia (Ooi et al., 1990 and Loke et al., 1992b).

Other biologically-based approaches to furthercomplement classical biological control involvedconsidering the potential use of beneficial plants, trapcrops, bioactive compounds (sex pheromones),botanical pesticides and F1 sterility. Results obtainedshowed that intercropping cabbage with tomato andCrotolaria striata reduced incidence and damage ofDBM on cabbage (Loke et al., 1993b). Crotolaria wasalso found to have beneficial effects on longevity ofC. plutellae. Investigation on Indian mustard, Brassicajuncea, as a trap crop indicated that it can be used ashedgerow in the cabbage ecosystem to provide habitatdiversity and dilute pest populations on cabbage, inaddition to helping to conserve natural enemies withinthe ecosystem (Sivapragasam and Loke, 1996).Research into the use of sex pheromones of DBM inMalaysia showed that these bioactive compounds areuseful as a monitoring tool in crucifer ecosystems butnot very effective and economical to apply as masstrapping and mating disruption tools (Irfan, 1996).Evaluation of neem extracts and formulations showedthat fresh water extracts of neem seed kernels wereeffective, mainly as an antifeedant, against Plutellaand Hellula (Loke et al., 1990a and Loke et al., 1995).The results also showed that neem possessed repellent,ovicidal and growth disrupting properties. The F1sterility method represent a pioneering effort for DBMcontrol in Malaysia. Studies showed that dosesbetween 150 and 200 Gy appeared to be suitable forinducing inherited sterility of DBM. Matingcompetitiveness of the irradiated males was not

is in line with the objective of minimizing insecticideusage.

The ETLs of the above IPM packages wereconsidered by many to be scientifically useful but notpragmatic for farmers. They are also unreliable insituations where multiple pest species infestationoccurs, which is often the case in Malaysia for open-cultivated crucifers. The common pest species besidesDBM are Hellula undalis, Spodoptera litura andPhyllotreta spp. (flea beetles). Studies were conductedto evaluate the effectiveness and practicality of usingPlutella Equivalent (PE) for pest counts:

1 Hellula larva = 4 Plutella larvae1 Spodoptera larva = 2 Plutella larvae

(3rd/4th instar)1 Spodoptera larva = 1 Plutella larva

(1st/2nd instar)1 Flea beetle = 1 Plutella larva

Results showed that the PE action thresholds are moresensitive and effective as compared to DBM actionthresholds (Md. Jusoh, 1996). However, itspracticability in field situations involving farmersremains to be further studied.

Besides studies looking into improving andrefining ETLs, further research on classical biologicalcontrol and other biologically-based control tacticswere also carried out as part of the dynamicdevelopment of DBM IPM. Currently, five species ofhymenopterous parasitoids are successfully reared inMalaysia. These are Cotesia plutellae, Diadegmasemiclausum, Diadromus collaris, Tricho-

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reduced. A release ratio of 10 irradiated DBM : 1 feralDBM was found to be effective (Dzolkhifli and Md.Jusoh, 1996).

ConclusionA substantial amount of time and resources have beendevoted to the research and dynamic development ofIPM for DBM in Malaysia. From initial efforts indeveloping empirical packages aimed at reducingpesticide application, endeavors have yieldedimproved and refined packages whereby biologicalcontrol and other biologically-based technologies areaccorded due emphasis and pivotal roles. For Malaysia,the cornerstone of DBM IPM can be considered asincreasing reliance on the use of self-regulating, livingor bio-based pest management components, asopposed to synthetic ones; of exploiting biodiversityto manage the pest, and to protect the local biodiversitywhich manages the pest, i.e. natural control andassisted biological control should be maximised,enhanced and relied upon to do the job whenever andwherever appropriate.

IPM of DBM should also draw from a ‘technologybasket’ and should not be rigid and biased towardsone tactic. It should be viewed as an overall ‘game-plan’ in which certain ‘set-pieces’ can be activateddepending on the occasion and logistics of thesituation. It is also important to acknowledge that IPMis not a perfect solution all the time and seasonalbreakdowns can and do occur, but over the longer termIPM should work favourably for all involved.

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