Newswise — PULLMAN, Wash. –According to a study on their potential dispersion, the colorful yet destructive Japanese beetle could naturally spread across the evergreen state in the next two decades if left unchecked.
These iridescent green-and-copper beetles have a habit of "skeletonizing" leaves, consuming all the soft green tissue between the veins of plants. With a diet encompassing over 300 different plants, they present a grave threat to Washington's agriculture, particularly for crops like grapes, hops, and cherries – some of their favorite targets.
David Crowder, an entomologist from Washington State University, warns that once these Japanese beetles become established, eradicating them becomes challenging. However, he believes it might still be possible to maintain control over their population.
"The success of these well-coordinated and intensive early efforts during the invasion is of utmost importance because, if we delay, the issue could become endemic," warned Crowder, the senior author of the study published in the Journal of Economic Entomology. He expressed hope that they can prevent the Japanese beetles from extending their reach beyond the current quarantine areas, at least in the foreseeable future.
According to the study's findings, the Japanese beetles are most likely to flourish in the dry and agriculturally rich southeastern part of the state, where they were initially discovered three years ago. If they manage to escape the existing quarantines in those regions, modeling predicts that they would probably spread across the area from Yakima to the Tri-Cities and move northwards, reaching past Moses Lake. Although the presence of the Cascades poses a geographical barrier, it's essential to note that there are still significant regions in western Washington that offer highly suitable habitats for these Japanese beetles.
Japanese beetles have already made their way across a significant portion of the United States, with their presumed arrival on the East Coast dating back to 1916. However, their spread into Western states has been more recent. Washington State had its first encounter with these beetles in 2020 when they were discovered in a parking lot in Sunnyside. Subsequently, in 2022, the Washington State Department of Agriculture successfully trapped over 20,000 beetles in both Sunnyside and Grandview. As of 2023, trapping efforts have indicated that the majority of the beetles remain confined to these areas, although there was one reported instance just outside of Seattle.
These findings demonstrate that quarantine zones have proven to be effective, as highlighted by the researchers. By implementing and adhering to the guidelines provided under these quarantine measures, such as ensuring that residential yard waste stays within the designated area and thoroughly cleaning agricultural trucks, the spread of Japanese beetles can be contained and controlled.
Although Japanese beetles possess the ability to fly, it is often human activities that facilitate their expansion into new regions.
Gengping Zhu, the study's first author and a research assistant professor at WSU, explained that while adults are easily noticeable, it is challenging to detect the beetles in their earlier life stages as eggs and larvae. As a result, unwittingly, people might contribute to their dispersal.
Japanese beetles have a life cycle that involves laying eggs near the soil surface, and much of their developmental phase is spent as grubs underground, where they feed on roots and organic matter in the soil. Upon maturing into beetles, they emerge to feed on plants, with some of their preferred choices being grapes, hops, and cherries. This preference for specific plants could be a plausible reason behind their initial appearance in southeastern Washington.
Upon their initial discovery in southeastern Washington, the state department of agriculture, in collaboration with federal agencies, promptly established quarantines to address the situation. To further comprehend the potential movements of these beetles, scientists from WSU have actively participated in this endeavor.
Controlling the spread of Japanese beetles requires collective efforts from both the agriculture industry and residents. David Crowder emphasized the significance of reporting beetle sightings and taking appropriate actions when they are found. Engaging citizens in this process plays a crucial role in preventing the spread of not only the Japanese beetle but also other invasive species. As climate change and increased human connectivity continue to pose challenges, problems with invasive species are expected to worsen. Crowder emphasized the need for coordination and early detection of such invasions, as it will be vital in addressing these issues more effectively.
More information on how to spot Japanese beetles and help prevent their spread can be found at: agr.wa.gov/beetles.
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