Three wasp species were released this summer to help control scarlet lily beetles in Michigan. The invasive species defoliates the stems, flowers, and leaves of the lilies.
The red beetles’ population has grown since their introduction to Michigan, becoming a pest for gardeners.
Marianna Szűcs, an associate professor in the Department of Entomology at Michigan State University, pushed for the biological control program in the state.
“The reason it's good to implement this biocontrol in Michigan is because it looks like Michigan is the westward front that they are spreading through,” she said. “We just want to prevent them from reaching more states, essentially.”
She said the beetles are likely coming from Ontario and will move to other states if they're not stopped in Michigan.
After years of permit approvals and some setbacks, during the 2026 field season, over 4,400 parasitoid wasps were released. These wasps lay their eggs in lily beetle larvae and after they hatch, eat the larvae from within. All three species were tested in previous studies and are not expected to prey on any other insects.
Szűcs said if the beetles die out from the predation, it's likely the wasps will follow after.
“That sometimes happens in biocontrol,” she said. “If they consume all the hosts, their population will crash.”
She said the wasps are very small species, but two of them are large enough to be seen. She said gardeners may start seeing the wasps if they grow lilies.
“If they squat and look at those feces-covered lily beetle larvae and they see a wasp probing it, they might have the biocontrol agent in their backyard,” she said. “In that case, it would be better not to spray or kill it but let them build up their populations.”
The program started in Europe, where the three wasp species were identified, and once the lily beetle was introduced into Massachusetts in 1992, the wasps were imported.
“Because it was already done there, all the approvals for bringing the insects into the country were already done and that’s a really arduous process,” she said. “So to bring it to Michigan, we didn’t have to go through all that process.”
However, there were still complications. After applying for the permits and notifying Michigan’s Department of Agriculture and Rural Development, they tried to collect the wasps from New England. When they went looking for the lily beetle’s larvae where they would find the parasitoids' eggs, they found the program had worked so well that locating them was too difficult.
The wasps then had to be shipped from Europe and put through a quarantine process. After several years, they finally had enough wasps to release them.
The North American Lily Society funded some parasitoid collections and helped gather volunteers for their release. Lily gardeners had to have large lily beds or plant them to participate. Some lily beds were also planted at the MSU research farm, she said.
After years, the release was successful and it is only a one-time release for now. She said it may take up to fifteen years to fully know if it's a success.
“Once they reach the point and they start to provide control, we don't have to do anything,” she said. “You don't have to apply pesticides anymore so that's the most sustainable and long-term solution. Not the immediate solution, but the long-term solution.”
She said research from New England found the parasitoids could clear up to 90% of the beetles.
“There is no specific insecticide that would only kill the lily beetle and insecticides also need to be repeated every year,” she said. “Once these parasitoids establish, they will sustain their population.”
