Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

_____________________________________________________________________Ecology of insect pests and natural enemiesnymphal stages. A nymph is a young insect thatresembles the adult except that they lack wings andthe nymph may be colored differently to the adult. Nopupal stage is present. Nymphs and adults usuallyhave similar habitats and have similar hosts. Eachnymphal stage is a bit larger than the previous stageand requires a molting or shedding of the outer skinbetween the stages. Incomplete life cycles can befound with bugs, grasshoppers and aphids.Insects’ growth rate depends on the temperature oftheir environment. Generally, cooler temperaturesresult in slower growth; higher temperatures speedup the growth process. If a season is hot, moregenerations of an insect may occur than during acool season.Incomplete metamorphosis: a flower bug:egg, 5 nymphal stages, adult(from: Hoffmann, 1993)Every insect species will have its own optimumtemperature for development. Some insects can liveand reproduce only at lower temperatures whereas others need high temperatures. That is why you willoften find other insect species in the tropics than in temperate regions. This also applies for plantpathogens.Understanding how insects grow and develop will contribute to their management. Some insects areactive predators or parasitoids during only one specific stage of their life. The hoverfly larvae, forexample, are voracious predators but the adults only feed on nectar from flowers. Other insects aresusceptible to certain biological or chemical insecticides during one specific stage of their life or none atall. Larvae of leafminers for example, are only found inside plant tissue. Spraying contact insecticides(unfortunately a frequent practice) is simply a waste of money because leafminers will not be affected.Understanding insect life cycles helps making sensible crop management decisions regarding pesticideuse.Insect Zoo: studying life cycles of insectsTo study different stages of a life cycle of insects, try rearingthe insects in an insect zoo. Although it may not be easy tostudy a full life cycle, it is possible to study some stages, forexample the stages that cause plant damage. Collect someinsects or eggs, pupae or larvae/nymphs from the field andput them in a glass or plastic jar with some fresh leaves froman unsprayed field. When studying life cycles of predators,feed them with the appropriate prey. Put some tissue paper inthe jar to avoid condensation.Close the jars with fine netting that permits air circulation and keep them in the shade.Insect zoos are also suitable to find out what insects (larvae/nymphs to adults) are emerging fromegg masses, and to rear larvae or pupae that you find in the field but don’t know what species theyare.Related exercises from CABI Bioscience/FAO Vegetable IPM Exercise Manual:4.1 Insect zoo4.A.1. Life cycle of caterpillar pests50Eggplant Ecological Guide