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 off decades of research in New England.
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."
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 very 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.
"Most biocontrol programs have a timeline of a minimum five years, but more into the decades," Szűcs said.
She pointed to New England, where similar releases took years before meaningful reductions in lily beetle populations were observed. Research has documented significant declines in beetle numbers and reduced damage at some sites.
"I wouldn't expect huge results or anything spectacular to happen at least five years, but more on the 10-15-year outlook," Szűcs said.
Despite the lengthy timeline, Szűcs believes the benefits outweigh the wait.
"Once these biocontrol agents establish, we can just forget about them," Szűcs said. "With pesticides, you have to repeat applications within the season and then annually."
Looking ahead, Szűcs hopes the project encourages broader acceptance of biological control and other non-pesticide approaches to pest management.
“We live in a world when everybody, everything has to eat, and we just have to accept this as the way of life, and we don't have to kill everything with insecticides to achieve the perfect fruit or the perfect lily,” Szűcs said. “That might be my life philosophy."
This story is brought to you as part of a partnership between WKAR and Michigan State University’s Knight Center for Environmental Journalism.