Record Number of Spongy Moths (Lymantria dispar) Found During MDA Annual Detection Survey
The increase in male moth detections does not necessarily indicate established populations
January 6, 2023
St. Paul, MN: The Minnesota Department of Agriculture (MDA) has announced its spongy moth (L. dispar; formally gypsy moth) monitoring program caught 101,763 male moths in 2022, far surpassing the previous state record high of 71,258 moths caught in 2013. Nearly 70% of the moths collected were in traps in Minnesota’s spongy moth quarantine area of Lake and Cook counties, these counties have been quarantined since 2014.
Spongy moths are ranked among America’s most destructive tree pests. The insect has caused millions of dollars in damage to forests as it has spread from New England to Wisconsin. Spongy moth caterpillars can defoliate large sections of forest and urban communities.
According to Kimberly Thielen Cremers, Plant Pest Regulatory and Mitigation Section Manager for the MDA, there is an important distinction that must be made in interpreting the latest survey results.
“While we did see a significant increase in male moth detections in traps this season, it doesn’t necessarily mean breeding populations of spongy moths have been established,” said Thielen Cremers.
The female spongy moth can’t fly. This limits species dispersal and establishment. Unlike other invasive species, detection of male spongy moths doesn’t mean the species is here to stay. It also doesn’t indicate that damage is already being inflicted to our forests.
The MDA monitors for the pests each spring by attaching thousands of small cardboard box traps to trees around the state. The traps have pheromone lures that mimic the scent of the female moth. In early fall, workers remove the traps and count the moths inside. Just over 19,000 traps were set in 2022. The MDA relies on survey data summarized over multiple years to identify isolated populations within the flux of annual male moth detections. It is this historical data, along with additional field surveys, that help identify isolated population establishment. Complete 2022 survey data is available on the MDA website.
When the MDA identifies isolated populations, it conducts treatments to eliminate the infestation or slow its establishment. Over the years, the MDA has eradicated dozens of infestations on thousands of acres across the state. Thielen Cremers noted that the department has been conducting population control treatments in the eastern half of Minnesota to slow the establishment of the pest into the state.
“The MDA has had over four decades of success in identifying, treating, and slowing the spread of this damaging forest pest into our state,” explained Thielen Cremers. The MDA is hopeful that future treatments and public adherence to pest mitigation regulations will control the spread and slow the establishment of future populations.
The MDA will work with federal, state, and local partners to develop treatment plans in response to the latest monitoring results. As always, residents of affected areas and other interested parties will have the opportunity to review and comment on draft treatment plans before they are finalized. More information about spongy moths and the MDA’s control efforts can be found on the MDA website.