Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

_____________________________________________________________________Ecology of insect pests and natural enemies4.1 IntroductionEcology is the study of interrelationships between organisms and their environment. The environment ofan insect consists of physical factors such as temperature, wind, humidity, light and biological factorssuch as other members of the species, food sources, natural enemies and competitors (organisms usingthe same space or food sources).temperaturewindother members ofthe speciescompetitorshumidityfood sourceslightnatural enemiesInsect ecology: the interrelationships between insect and environmentThese interrelationships explain why insect pest species cannot in all circumstances grow to largepopulations and damage crops. There may be large numbers of predators that eat the pest insects. Theweather conditions may be unfavorable for a quick life cycle because insects usually like warm, dryweather. The plant variety may not be very attractive for the pest insects to eat. And there may be manymore reasons.In Agro-Ecosystem Analysis (AESA), insects are considered as populations rather than individuals. Onesingle insect that eats an eggplant leaf will never cause yield loss in a large field but a population of tenthousand leaf-eating caterpillars may do.Learning to recognize natural enemies and understanding how they work, and how their impact can bequantified, is very important in pest management. Natural enemies do nothing but reduce pestpopulations, that is why they are called the “Friends of the farmer”! The work of natural enemies canreduce the need for pesticides. This saves money and time, and is better for the environment and forhuman health.In many areas, the use of pesticides is still a common practice for insect and disease control. Mostpesticide sprays are very toxic to natural enemies whereas pest insects often develop resistance. Thedeath of natural enemies means that pest insect species can increase in number very rapidly. Normally,natural enemies will remove a large number of the pest insects. When there are no natural enemies, thepest insect population can grow rapidly, especially when there is a lot of food available, like in large fieldsgrown with the same crop, or in areas with many smaller fields grown with the same crop. When the pestinsect population is very large, more insecticides will be used. Life cycles of natural enemies generallytake longer periods of time to complete than those of pest insects. Once insecticides are being used inthe ecosystem, it is difficult to bring back the natural enemies within one season. Insecticides should beused only when there are no other options for control and there is a definite and visible need. This is oneof the important reasons to monitor fields regularly (modified from Hoffmann, 1993; and Weeden, www2).4.2 Insect anatomyInsects have three body regions: head, thorax, and abdomen. The head functions mainly for food andsensory intake and information processing. Insect mouthparts have evolved for chewing (beetles,caterpillars), piercing-sucking (aphids, bugs), sponging (flies), siphoning (moths), rasping-sucking(thrips), cutting-sponging (biting flies), and chewing-lapping (wasps). The thorax provides structuralsupport for the legs (three pairs) and, if present, for one or two pairs of wings. The legs may be adaptedfor running, grasping, digging, or swimming. The abdomen functions in digestion and reproduction.48Eggplant Ecological Guide