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Pesticides and Water Quality

Natural Enemies

Parasitic wasps

In contrast to predators who eat their prey, small parasitic wasps (called parasitoids) lay eggs inside or on the body of their host. Typically only one egg is deposited in one host, but parasitoids can lay hundreds of eggs a day. Parasitoid larvae (immatures) develop by feeding and killing the host.

Because most parasitoids are small and spend much of their lives hidden within their hosts, many people are unaware of how common and important they are in the control of insect pests.

Avoid broad-spectrum insecticides that can kill parasitic wasps and other natural enemies are in your landscape.

Many species of tiny wasps lay their eggs in pests like aphids or caterpillars; their hatching larvae consume the pest and kill it.

Life cycle of an aphid parasite

Aphid parasistoid

A. An adult parasite lays an egg inside a live aphid. B. The egg hatches into a parasite larva that grows as it feeds on the aphid's insides. C. After killing the aphid, the parasite pupates. D. An adult wasp emerges from the dead aphid, then flies off to find and parasitize other aphids.

Parastiic wasps
A parasitic wasp, Trioxys pallidus, parasitizing a walnut aphid

Mummified aphids killed by parasitoids
Mummified aphids are the result of being parasitized by a parasitic wasp. The holes in the mummies show where the fully-grown wasp emerged. Mummies may be bronze or black depending on parasite species.

Visit the Natural Enemies Gallery and the Biological Control Pest Note for more information on parasites.


Statewide IPM Program, Agriculture and Natural Resources, University of California
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