Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

__________________________________________________________________________________Major Eggplant Insect PestsNatural enemies• Predatory mite Amblyseius cucumeris. This predatory mite eats various thrips species; both hatchingeggs and larvae. Predatory mites also eat spider mites, several other mites, honeydew and pollen.Very good results are obtained in various countries with release of this predatory mite for control ofspider mites and thrips. In Indonesia for example, Amblyseius cucumeris was introduced from theNetherlands, where it is commercially available, for testing its effect on Thrips parvispinus on hotpeppers.• Natural enemies of Thrips palmi had not been recorded from Southeast Asia until they werediscovered in Thailand during 1987-88. Among eight species discovered, the larval parasitoidCeranisus menes, a wasp, the larval predator Bilia sp., and Orius sp., both bugs, were evaluated aseffective natural enemies of T. palmi in Thailand. Neither classical biological control of T. palmi norinundative release of its natural enemies is considered necessary for South East Asia because T.palmi is native to this region and should have effective natural enemies in this region. Studies inThailand and Japan support the view that the increase of Thrips palmi is due to the exclusion ofnatural enemies after insecticide application.• Lacewings (Chrysopa sp.) are predators of thrips. The green lacewing, Chrysopa carnea, is the mostcommon species. Because larvae of lacewings are generalist predators, (larvae feed on thrips,whitefly, aphids, jassids, and small caterpillars) they can be used in a wide variety of agriculturalcrops. In various countries, lacewings are commercially available.• There seem to be fungi that attack thrips. Fungal infestation however, requires high humidity andthrips are important mainly in the dry season. The potential for pathogens for the control of thripsseems therefore not very high.Parasitism of thrips on eggplant in ThailandIn a field survey, 40 – 60% parasitism of thrips by Ceranisus menes was found in eggplant gardens,which were not treated with insecticides. In commercial production fields sprayed with insecticides,no parasitism was found. The survey also showed that the thrips population was always higher in thesprayed than in the unsprayed plots (Hirose, in Talekar, 1991).This, at first sight controversial, phenomenon can be explained as follows. Insecticide applicationmay kill part of the thrips population but will seldom eradicate all thrips. Parasitoids are moresensitive to pesticides and usually need more time to build up an effective population. By the time asmall new population of parasitoids is build up, the thrips are already abundant and damage to thecrop may occur.AND, to make it all worse: in fields where thrips were not a problem before, they can become amajor pest after insecticide applications. Again, this is because the natural enemies of thrips arekilled and thrips can expand into damage causing levels.Insecticides used for the control of pests other than thrips in fact contribute to its resurgence….Some scientists say that the increased incidence of Thrips palmi in Southeast Asia could be theresult of increased insecticide applications in some areas of this region for the past 10 years.Management and control practicesPrevention activities:• Resistant varieties: Differences in varietal reaction to thrips attack have been recorded in a number ofvegetables, but not in eggplant. The erratic nature of thrips infestation makes screening for host-plantresistance in eggplant difficult. The breeding for resistance of eggplant to other insect pests such asfruit and shoot borer, which in most areas is the most serious insect pest of eggplant, should bestrengthened. Crop varieties resistant to these pests will reduce the need for the use of insecticides.Non-chemical control of other pests will similarly help preventing thrips outbreaks.88Eggplant Ecological Guide