Beneficial Insects at Work in Your Cereals

Beneficial Insects at Work in Your Cereals

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Are those pests or beneficial insects at work in your fields? Sometimes the answer is just a phone call away. John Gavloski, entomologist with Manitoba Agriculture, received several calls in July from agronomists seeking information about clusters of silky-covered eggs spotted at the top of many cereal heads.

As he explains, the clusters were not eggs, but clusters of pupal cases of a parasitic wasp called Cotesia. “They’re actually a parasitoid of caterpillars such as armyworms, which were a problem in some cereal fields in Manitoba in 2019,” says Gavloski. Parasitoids lay eggs into other insects and eventually kill them.

For example, Cotesia wasps will lay 20 to 60 eggs into an armyworm (or other caterpillar) and inject it with a virus, which shuts down the pest’s immune response. Because the eggs develop at exactly the same time, Cotesia larvae emerge out of the caterpillar almost simultaneously. They then rapidly form their cluster of pupae, which can easily be misidentified as a cluster of eggs.

Gavloski assures agronomist callers that the only thing Cotesia larvae feed on is other insects, which can help reduce the pest population. For this reason, he likens them to “insect superheroes.”

Gavloski says growers and agronomist can protect Cotesia and other beneficial insects by following three practices. “Step one is only using insecticides if you’re above the pest’s economic threshold,” he says. “Second, use a more selective insecticide – one that protects parasitic wasps.” Finally, because parasitic wasps feed on nectar in the adult stage, there is value in having flowering plants around the farm site.

Visit FieldHeroes.ca or follow @FieldHeroes on Twitter for more about the benefits of protecting beneficial insects.

 

Content provided by Synthesis Network