Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

__________________________________________________________________Major Natural Enemies of Eggplant Insect Pests☼ Sunshine and Bt, not a good match...!?The Philippines highland vegetable FFS programme included a specific experiment for farmers toobserve the effect of sunlight on the efficacy of Bt products. They compared feeding and death rateswhen diamondback moth larvae (Plutella xylostella) were placed on cabbage leaves which had beensprayed with Bt at different times of day and hence received different sunlight exposures. Theresults showed that sunlight deactivates Bt. By discussing the results, the farmers were able todecide the best time of day to apply biopesticides, avoiding application when the sun is strongest(CABI, 1996).ConservationThe Bt formulation strictly speaking, is a chemical insecticide, and is applied like an insecticide. Btformulations become inactive after one to three days. That means the bacterium inside the formulation isdead. Bt spores do not usually spread to other insects or cause disease outbreaks on their own.Therefore, conservation methods, as is important for predators and parasitoids, are not relevant for Bt.Testing Bt: a case from Dalat, VietnamTesting Bt is not like testing chemical insecticides. In pesticide studies, usually the number orpercentage of dead caterpillars is counted. Bt works differently from pesticides. It is important to helpfarmers recognize that Bt is working if there is less damage on the leaf, less frass production, andless caterpillar activity. Therefore, a different scoring system is needed to analyze data from Bt trials.Caterpillars affected by Bt do not die immediately. They usually stop feeding after 6 hours. Thisresults in less damage to the leaf and less frass production. At 24 hours after exposure to Bt, larvaeare dying: they do not move much and are lethargic. Larvae die after about 3 days.For Bt trials studying the effects of different types of Bt on DBM, the following scoring system toevaluate larval activities after Bt sprays was found to be very useful by farmers in Dalat, Vietnam:A. Leaf damage 1 = low 2 = moderate 3 = highB. Frass production 1 = none 2 = little 3 = muchC. State of DBM larvae 1 = dead 2 = dying 3 = activeFarmers in Dalat were very excited about this scoring system because it provided a betteropportunity to study how Bt works. They observed that just counting dead caterpillars in Bt studies isnot enough and may even lead to a false conclusion (Ooi, 1999).6.3.2 FungiThere are fungal species that can infect and kill insects. These fungi are calledinsect-pathogenic fungi or entomopathogenic fungi. These fungi are very specificto insects, often to particular insect species, and do not infect other animals orplants. Most insect-pathogenic fungi need humid conditions for infection anddevelopment but some fungus species can also infect insects when it is dry.There are also fungal species that infect and reduce fungi that cause plantdiseases. These are called antagonists. An example of an effective antagonist is Trichoderma(Gliocladium). This section describes insect-pathogenic fungi only. Antagonists are described in section7.10.There are several fungal species naturally present in ecosystems and these may control some insectspecies when conditions like humidity and temperature are favorable. Such fungi can spread quickly andsome may also control sucking insects like aphids and whiteflies that are not susceptible to bacteria (e.g.Bt) and viruses. Management practices may be focused on preserving and possibly augmenting thesenatural enemies. Some fungi are commercially available in some countries in formulations that can beapplied using conventional spray equipment. Some experiences from Asia are listed below.111Eggplant Ecological Guide