Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

__________________________________________________________________Major Natural Enemies of Eggplant Insect Pests6.2.1 Trathala sp.Host: eggplant fruit and shoot borer, many other insects – larvae.During trials in Bangladesh, the small wasp Trathala sp. was found laying eggs inside the larvae ofeggplant fruit and shoot borer (FSB). Instead of an FSB adult, one small wasp adult emerges from oneFSB pupa. This wasp was only found in the unsprayed plots, as it was very sensitive to chemicalpesticide sprays.Parasitism levels of FSB larvae by Trathala mostly remain low.In a 1998 field study in Bangladesh, parasitism of FSB byTrathala sp. was less than 20% overall. Similarly, in fieldstudies in India, parasitism of FSB larvae by Trathala flavororbitalisreached a maximum of 20% in July-August. Otherrecords from India (Haryana) mention a peak in parasitism of18% of the FSB larvae (Naresh, 1986), and in Bihar, parasitismby this wasp in the field varied from 3.5% in February to 9% inNovember (Mallik, 1989).Adult Trathala sp.The ichneumonid wasp Trathala flavo-orbitalis is an often reported parasitoid of several importantagricultural pests. It was found to be a parasitoid of the eggplant fruit and shoot borer in several countriesin Asia, e.g. India and Sri Lanka. The little wasp is also found to be parasitizing other important insectpest species including the rice leaffolder Cnaphalocrocis medinalis, the cabbage webworm, Hellulaundalis, the sesame pest Antigastra catalaunalis and even a pest of pear, Numonia pyrivorella.Some of the research findings with regard to life cycle and development of Trathala flavo-orbitalis aresummarized below. Most of this research has been done in laboratories, not in the field.The FSB has five larval instars (some references claim there are 6 instars). All instars were ‘attacked’ byTrathala, by laying eggs into the larva (stinging). All first and about 50% of 2 nd -instar larvae that werestung were mutilated and died as a result. Successful parasitoid development up to adult emergenceoccurred mostly in 3 rd -, 4 th - and 5 th -instar host larvae. When given a choice of instars for oviposition, T.flavo-orbitalis avoided all 1 st - and most 2 nd -instar larvae, while 3 rd - to 5 th -instar larvae were equallyaccepted (Sandanayake, 1992).The ovipositor (egg-laying tube of a female insect) of Trathala is quite long and the female is able tolocate a larva inside an eggplant fruit. The parasitoid can sting through the fruit and put its egg into thelarva inside a fruit. When eggplant fruits are large, the parasitoid is probably not able to reach larvaeinside the fruits.The total time for development of the parasitoid was about 20-24 days andthis was similar whichever larval instar (2 nd to 5 th ) was parasitized. Theparasitized host at pupation contained different stages of the parasitoid,differing in this respect from most other species of larval-pupal parasitoids.Parasitism increased the host pupal period to 11-18 days, as compared with6-14 for healthy pupae. Adult parasitoids lived for 4-7 days in the laboratory(Mallik, 1989).Research findings suggest that Trathala may be a valuable addition to naturalcontrol of the eggplant fruit and shoot borer. However, more field data arerequired to determine effectiveness.Adult Trathala sp.(from: AVRDC,www35)6.2.2 Eriborus sinicusHost: eggplant fruit and shoot borer - larvaeEriborus sinicus, an ichneumonid wasp, is a parasitoid of eggplant fruit and shoot borer (FSB). In a fieldstudy by AVRDC, a large vegetable research institute in Taiwan, it was found that this little wasp is apotential natural enemy of FSB. Whether this natural enemy is native to other regions in Asia and whatits efficiency is for control of fruit and shoot borer has yet to be determined.106Eggplant Ecological Guide