Parasitic Wasps

Generally speaking, most people would not think of wasps as a beneficial insect. However, a certain group of wasps, known as parasitic wasps provide a beneficial service to humans and are nothing like their stinging cousins. Parasitic wasps are from the order Hymenoptera, and several hundred different species have been identified.

Parasitic Wasp

Most parasitic wasps are small to medium sized and usually black or brown in color, though some come in startling metallic blue or bright orange. Parasitic wasps get their name because they spend part of their developmental time as a parasite living inside another insect. Parasitic wasps tend to be very specialized in selecting their hosts, so using them for specific insect control is a very real possibility. For example, the braconid wasp attacks mainly the tomato hornworm and other caterpillars.

The life cycle of parasitic wasps differs based on species, but most start their lives inside a host. The adult female will deposit her eggs inside the body of a host using a long ovipositor that inserts the eggs without killing the host. In many species, the eggs will hatch inside the host and the larvae will continue to grow while the host lives, killing it only when it comes time to pupate. Some parasitic wasps begin life outside of a host and enter the host during the larval stage, later pupating inside the host.

Some parasitic wasps lay their eggs inside other insect eggs including other wasp eggs. Those that lay their eggs inside the eggs of other insects are called insect eggs parasite wasps, while those that lay their eggs within other wasp eggs are called cuckoo wasps. In both cases, when the parasitic wasps emerge, it feeds on the other eggs and larva of the host species.

Still other parasitic wasps lay their eggs inside a host oothecae. An oothecae is an egg casing from which many small nymph insects emerge. Mantids and cockroaches form oothecae to protect their eggs, and both are hosts for parasitic wasps. For example, the hatchet wasp is a small, black parasitic wasp that specializes in cockroaches as a host.

Many species of parasitic wasps are available for home gardeners to purchase. Some of the most common are the aphid parasites which lay their eggs inside aphids causing them to swell, harden, and die. Fly parasites specialize in fly pupae, laying their eggs within the pupae of pest flies like the common housefly and stinging flies. Trichogramma wasps specialize in caterpillars of moths and butterflies. While many people consider butterflies beneficial and beautiful, in large quantities, they can be destructive and require control. Other commonly available species include whitefly parasites and leafminer parasites.

Because parasitic wasps are so specialized, they tend not to be nuisance insects. Some parasitic wasps that specialize in wood-boring beetles have been noted inside homes after traveling in on firewood, but they do not sting or otherwise harm humans.

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Texas A&M Agrilife Extension: Parasitic Wasp
Iowa State University Department of Entomology: Parasitic Wasps
Brisbane Insects: Parasite Wasps
Planet Natural: Beneficial Insects

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