KANSAS CITY, Mo. — Some of Missouri’s smallest wasps may also be among the most useful insects working in gardens and landscapes.
Parasitoid wasps provide a natural form of pest control by targeting insects including aphids, caterpillars and beetles. Unlike the wasps homeowners typically notice around yards and buildings, these tiny beneficial insects generally do not sting people.
The wasps reproduce by laying eggs in or on a host insect. Developing larvae feed on that host, eventually killing it and emerging as a new generation of beneficial wasps.
University of Missouri Extension horticulturist Tamra Reall says one advantage is how precisely many parasitoid species target pests. Some specialize in a single insect species or a small group of closely related insects, allowing them to suppress pests without harming large numbers of other insects.
Missouri homeowners may already have parasitoid wasps working in their yards without realizing it.
One sign is an aphid that appears swollen and turns tan or bronze. Often called an aphid mummy, the dead aphid contains a developing parasitoid wasp.
Caterpillars provide another visible clue. Small white cocoons attached to a caterpillar can indicate it has been parasitized. Reall recommends leaving those caterpillars in place rather than killing or removing them. The caterpillar has generally stopped causing plant damage, while the developing wasps can emerge and begin searching for additional pests.
Rather than purchasing parasitoid wasps and releasing them, homeowners can encourage populations already living in the area.
Adult wasps rely on pollen and nectar for food. Maintaining flowering plants from spring through fall can provide a steady food source and help beneficial insect populations remain established.
Reducing unnecessary pesticide applications is also important. Broad-spectrum insecticides can kill natural predators and parasitoids along with the pests being targeted.
Reall recommends homeowners identify insects before reaching for an insecticide and watch for signs that natural biological controls are already working.
For Missouri gardeners, a few aphid mummies or white cocoons on a caterpillar could mean some of the yard’s pest-control work is already being handled naturally.
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