Pests in Gardens and Landscapes: Quick Tips

Parasites of Insect Pests

Published   5/20

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A parasite is an organism that lives and feeds in or on a larger animal (host). Nearly all insect pests have at least one parasite that attacks them. Insects that parasitize other invertebrates are parasitic only in their immature stages and kill their host just as they reach maturity. Most insect parasites (sometimes called parasitoids) are host-specific wasps or flies, and many are so small that often you won?t see them. An adult parasite can lay eggs in hundreds of host individuals, resulting in the reduction of pest numbers.

Aphid parasite   Adult female wasp

Life cycle of an aphid parasite (left). The adult female wasp (right) lays one egg in each aphid host; the egg develops into a larva, which feeds inside of and kills the aphid. The wasp larva pupates then emerges as an adult wasp.

Parasitized aphids   Aphid mummy

Parasitized aphids (left) die and turn into crusty “mummies” that can be black or beige. The hole in the aphid mummy (right) indicates a parasite has emerged.

Wasp larvae   Exit hole

The blackish scale insects on the twig at left are discolored because wasp larvae are developing within. Once parasites mature into adults, they emerge through an exit hole (right).

Whitefly parasites   Whitefly parasites

Some whitefly parasites turn hosts black; others do not. A good way to detect parasitization is to look for round exit holes in whitefly nymphs. A T-shaped slit indicates that a healthy whitefly emerged (far left). A circular hole indicates a parasite emerged (right).

Predaceous ground beetle adults   Predaceous ground beetle larvae

Caterpillar parasites include the Hyposoter exiguae wasp shown here laying an egg in an armyworm (left). Pulling apart parasitized caterpillars can reveal the wasp larva within (right).

Assassin bugs attack almost any insect.   Pirate bugs

Two signs of parasitized redhumped caterpillars: A Cotesia wasp forms external white cocoons (left) while a Hyposoter wasp pupates within its host (right), causing discoloring and distorting.

Western predatory mites   Sixspotted thrips

Some parasites, such as this Goniozus legneri on a navel orangeworm (left), lay many eggs externally on a host resulting in multiple wasp larvae feeding on a single caterpillar (right).

Spiders   Praying mantids

Some parasites attack insect eggs, such as the Trissolcus wasp at left laying eggs in a stink bug egg cluster. The black corn earworm egg at right is dark because a Trichogramma wasp larva is developing inside. White eggs pictured are not parasitized.

Adults of predatory wasps   Syrphid fly (flower fly, hover fly) adults

Tachinid flies (left) parasitize many types of insects. Tachinid eggs laid on the caterpillar at right will hatch and, as larvae, bore into the host. Some tachinids lay eggs on plants and enter their insect hosts by being eaten.


Minimize the use of pesticides that pollute our waterways. Use nonchemical alternatives or less toxic pesticide products whenever possible. Read product labels carefully and follow instructions on proper use, storage, and disposal.

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