Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

_____________________________________________________________________Ecology of insect pests and natural enemies The Predator Appetite Test…!Catch a predator, e.g. a spider, ladybeetle or a hoverfly larva, and place it carefully in a jar, togetherwith some fresh leaves and a paper tissue to avoid condensation of water. Put a leaf with a knownnumber of prey in the jar, e.g. 20 aphids.Take another jar and place a leaf with the same number of aphids inside, but withoutthe spider, ladybeetle or hoverfly. This is the control, to see how quickly a group of20 aphids can multiply.After 2 or 3 days, count the number of aphids alive in both jars. Discuss if thepredator has eaten the prey and how effective it will be in field situations.Appetite is one factor to determine effectiveness. Ladybeetles, for example, are effective predatorswhen pest populations are high. They are thought to be less effective at lower pest densities.In case of parasitoids, the number of adults emerging from one host (the pest insect) can be animportant factor to determine efficiency. Many adults emerging from a pest insect can each againparasitize a new host. This way parasitoid population builds up more rapid than when only one adultemerges from a host.Related exercises from CABI Bioscience/FAO Vegetable IPM Exercise Manual:4-D.1. Predation on sucking insects in insect zoo4-D.2. Cage exclusion of natural enemies in the field4.7. Direct observations of consumption rates of predators in the field4.5. Studying predators in the field.4-A.5. Measuring the parasitism level of caterpillars4.9 Managing natural enemiesJust as the crop and pest insects are managed, natural enemies also must be managed. There aremanagement practices that kill pests but also kill natural enemies. It is obvious that managementpractices for natural enemies should be focused on preserving them and as much as possible increasingtheir numbers. Indigenous natural enemies are adapted to the local environment and to the target pest,and their conservation is generally simple and cost-effective. Natural enemies that are introduced fromoutside (for example those that are reared in insectaries and released into the field), often require adifferent way of augmentation. Conservation methods are often similar.Some techniques for conservation and augmentation of natural enemies:1. Allow some insect pests in the field: these will serve as food or as a host for natural enemies.Eggplants can compensate for quite some injury and not all insect feeding results in yield loss.Monitor the field regularly!2. Be extremely careful when using pesticides: most pesticides (even several fungicides!) are toxic tonatural enemies. Even pesticides that claim to be very selective and harmless to natural enemies maystill cause problems. You can test this yourself! See box below.3. Do not use insecticides before there is a serious infestation of a pest insect. Don’t apply “just incase” or “because my neighbor is also spraying”. This is not only a waste of money but may actuallyresult in MORE problems with pest insects because they can increase their population quickly whenthere are no natural enemies around.56Eggplant Ecological Guide