An invasive beetle is continuing to spread across Michigan, and scientists at Michigan State University want to hear from you if you spot it.
The lily leaf beetle, also known as the scarlet leaf beetle, is an invasive insect that feeds on the leaves, stems, and flowers of lily plants.
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Originally from Eurasia, it has been spreading across North America for decades and is continuing to spread across Michigan.
Which plants are at risk?
The beetle’s preferred targets are plants in the Lilium and Fritillaria families. If you’re growing tiger lilies, Easter lilies, Asiatic lilies, oriental lilies, or fritillaries, those plants face the greatest risk of serious damage, according to an article from MSU Extension.
The beetle can also cause minor feeding damage on a wider range of plants, including lily of the valley, Solomon’s seal, hollyhock, hosta, and even potato plants.
The lily leaf beetle doesn’t attack daylilies, calla lilies or canna lilies.
Lifecycle of lily leaf beetles
Adults spend the winter buried in soil or leaf litter, then emerge in early spring to start laying eggs, according to MSU Extension.
A single beetle can lay between 250 and 450 eggs, depositing them in small, irregular rows on the undersides of leaves.
After hatching, which takes just one to two weeks, the larvae feed aggressively for up to 24 days.
The orange-green colored larvae cover themselves in their own excrement to deter predators.
The adults have a single generation and live for several weeks before they go back into the soil, typically near lilies.
How it got here and how it spread
The lily leaf beetle first turned up in North America in Montreal in the 1940s.
It crossed into the United States in 1992, and by the mid- to late 1990s, it had spread rapidly across New England, according to MSU Extension.
The movement of plant bulbs between countries is believed to be the primary way the beetle has traveled so far, so fast.
Michigan got its first confirmed detection in 2016 in Jackson County.
By 2022, the beetle had spread significantly across Southeast Michigan, triggering a wave of reports to MSU Extension.
What Michigan scientists are doing about it
Michigan State University scientists are actively studying how far the beetle has spread and whether a biological control program, one that proved effective on the East Coast, could work in Michigan.
Researchers at the University of Rhode Island had success using a small parasitoid insect that targets lily leaf beetle larvae, significantly reducing beetle populations in that region.
The beetle is widespread across Southeast Michigan, but gardeners in other parts of the state who spot the beetle are asked to report sightings, with photos of plant damage, to the Midwest Invasive Species Information Network.
How to protect your garden
Because this beetle has no significant natural enemies in North America, control falls largely on the gardener. Here are the main options:
- Hand-picking: If only a few beetles are present, removing them by hand and dropping them in soapy water can help.
- Contact insecticides: Products containing permethrin, cyhalothrin, deltamethrin, pyrethrin, or spinosad have shown strong results. Azadirachtin (neem oil) and insecticidal soaps can also help control young larvae.
If your plants are flowering, always read the pesticide label carefully and follow directions to avoid harming bees and other pollinators.