How MSU is using wasps to fight invasive beetles

LANSING — Michigan State University researchers have launched a long-term effort to combat the invasive scarlet lily beetle, using specialized wasps instead of pesticides to reduce populations of the destructive garden pest.

The scarlet lily beetle is an invasive insect that feeds on lilies, damaging leaves, stems and flowers. Heavy infestations can completely defoliate plants in a matter of weeks, making the pest a growing concern for gardeners.

To combat the beetles, more than 4,400 parasitoid wasps that lay eggs inside scarlet lily beetle larvae were released across Michigan. Parasitoids develop inside a host insect and ultimately kill it.

Marianna Szűcs, an associate professor in MSU’s Department of Entomology, said launching the first release of lily beetle biocontrol agents in the Midwest took years of planning and coordination and builds on decades of research in New England.

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Researchers officially began preparing for the project in 2022 by establishing lily beds at the MSU Entomology Research Farm. The plots were designed to serve as nurseries for future biological control efforts.

“The lily beetles found them on their own,” Szűcs said. “They already made it their home by the time we got parasitoids.”

A red bug on a leaf. — Adult scarlet lily beetle. (Courtesy of Sheila Babbitt/ Michigan State University)

Researchers originally hoped to collect parasitoids from established populations in New England, but a collection trip in 2023 was unsuccessful because the containment efforts were so effective that there were few lily beetle larvae left for the wasps to lay eggs in.

“We tried to collect parasitoids, and what we found is that there were so few lily beetle larvae that we were unsuccessful collecting enough parasitoids to start a large-scale field release and a biocontrol program,” Szűcs said.

Instead, researchers worked with collaborators and supporters of the program to obtain parasitoids for release in Michigan.

In addition to the research farm, volunteers recruited by the North American Lily Society helped create release sites across the state by planting lilies in their own gardens.

“The North American Lily Society recruited volunteers who planted over 100 bulbs, lily bulbs, in their gardens,” Szűcs said. “They planted those lilies, taking up space and everything in their garden just to see them being eaten by the beetles because they were not allowed to treat them with any insecticides or anything.”

Szűcs said extensive testing showed the wasps do not pose a threat to other species.

“With biological control, we try to reestablish the natural environment where you have the host and their parasitoids, but we have to also make sure that these are very host-specific parasitoids that we release,” Szűcs said.

Before the releases could occur, the project required approval by federal and state agencies, including the U.S. Department of Agriculture and the Michigan Department of Agriculture and Rural Development.

Researchers emphasize that biological control is a long-term strategy. Unlike pesticides, which can produce immediate results, it may take years for parasitoid populations to take hold and suppress beetle numbers.

Szűcs said extensive testing showed the wasps do not pose a threat to other species.

Demonte Thomas is an environmental reporting intern at WKAR as part of a partnership between WKAR, Capital News Service and Michigan State University’s Knight Center for Environmental Journalism.

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