Part of the series ‘Biological control in Missouri: Right tool, right place, right conditions.’
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Braconid wasp pupae using tobacco hornworm as a host. Parasitoid wasps play an important role in keeping gardens and landscapes healthy. Cut back on pesticide use when you see signs of parasitism for a healthy yard and environment. Photo by Tamra Reall.
KANSAS CITY, Mo. – Parasitoid wasps, or parasitic wasps, may be tiny, but they play an important role in keeping gardens and landscapes healthy. These small, non-stinging allies develop in or on the bodies of insects such as aphids, caterpillars and beetles, eventually killing the host while producing the next generation of wasps.
What makes parasitoid wasps especially fascinating is their precision, says University of Missouri Extension horticulturist Tamra Reall. Many species attack only one or a few closely related insect hosts. “That means when the right host is present, these wasps can provide highly effective biological control,” says Reall.
“In Missouri landscapes, they’re hard at work even when we don’t notice them,” she says. One clue that parasitoid wasps are on patrol is the appearance of aphid “mummies”—swollen, tan or bronze-colored aphids that hold developing wasps inside. On caterpillars, you might see small white cocoons attached to the outside of the body. When you spot these, the caterpillar is no longer feeding and should be left alone so the next generation of wasps can emerge and continue their work.
Unlike other biological controls, parasitoid wasps usually aren’t purchased for home release. Research shows the best approach is simply helping the existing population thrive. Adult wasps depend on nectar and pollen, so landscapes rich in flowering plants and free from broad-spectrum insecticides encourage their presence. Even small garden beds with blooms throughout the growing season can significantly improve natural pest control.
“In many Missouri landscapes, parasitoid wasps are already providing biological control," says Reall. "By protecting their habitat and minimizing unnecessary insecticide use, we can have healthier, more resilient landscapes.”
Reall’s tips for success
- Don’t spray every insect you see.
- Leave caterpillars with visible cocoons.
- Plant a variety of flowers that bloom from early spring through fall to feed adult wasps.
- Leave parasitized caterpillars with cocoons in place so wasps can mature and emerge.
- Cut back on pesticide use, especially when you notice signs of parasitism.
- Watch for aphid mummies and caterpillar cocoons as a sign that biological control is underway.
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Braconid wasp pupae using tobacco hornworm as a host. Parasitoid wasps play an important role in keeping gardens and landscapes healthy. Cut back on pesticide use when you see signs of parasitism for a healthy yard and environment. Photo by Tamra Reall.
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