Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

__________________________________________________________________Major Natural Enemies of Eggplant Insect Pests6.1.4 Hoverflies - SyrphidaeHoverflies are also called syrphid flies or flower flies.Primary prey: aphids, small caterpillars, sometimes thrips, possibly jassidnymphs.Predatory stages: only larvae of hoverflies are predators.Description and life cycleAdults of the hoverfly eat pollen and nectar from flowers. Only the larvae are effective aphid predators.The adult hoverflies look like bees or wasps and are usually seen near flowers. Many species havecompact, flattened bodies, large eyes and black and yellow stripes on the body. They vary in size from 9- 18 mm.The female lays single, small (about 1 mm), white eggs that lie flat on leaves or shoots near or amongaphid populations. Females can lay several hundred eggs. The larvae hatch in 2 - 3 days. The larvae aresmall maggots without legs, they look more like tiny slugs than adult hoverflies. They vary in color fromcream to green to brown, depending on the species and the prey consumed. There are 3 larval instars.The larvae suck out the inside liquids of aphids and small caterpillars until only the skin remains!Life cycle of a hoverfly(from: Hoffmann et al, 1993)In about 2 weeks, the larva develops into a pupa which usually is pear-shaped and is cream, green orbrown in color. The pupa is attached to leaves or stems, sometimes in the soil.The period from egg to adult varies from 2 to 6 weeks, depending on the temperature, species andavailability of aphids. If there are many aphids for the hoverflies to eat, there can be more generations.EffectivenessLarvae of the hoverfly are voracious eaters. One larva may eat up to 400 aphids during its development!On a small scale, larvae can keep aphid populations in check but it is unknown if they manage to controlaphids in large fields.Life cycle and predation efficacy hoverfly: a study exampleWhen you know how many prey the different larval instars of the hoverfly larvae eat in a day, youcan calculate the efficacy during the whole larval stage. Collect the smallest sized hoverfly larvaethat you can find (using a wetted hair brush to handle them). Rear them in separate pots (or theymight eat each other!) and feed them with fresh aphids every day. Handle the hoverfly larvae as littleas possible. Observe the changes in size, color and shape as the larva develops and note down theduration of each larval stage. Count how many days it takes for the hoverfly to develop into a pupa.Once it has become a pupa, it stops feeding.Calculate the total number of prey consumed of one larva with the results of the previous trial(number of prey consumed per day per life stage x number of days the life stage takes).101Eggplant Ecological Guide