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Japanese beetles could spread across Washington State within 20 years

The Japanese beetle, a colorful yet destructive insect, poses a significant threat to Washington State's . These green-and-copper beetles cause harm by devouring plant leaves, leaving only the veins intact. With an appetite for over 300 plant species, including grapes, hops, and cherries, they can wreak havoc on crops.

A study suggests that without intervention, the Japanese beetle could spread across the state within two decades. Eradicating them once established becomes challenging, but it might be possible to control their population through early, coordinated efforts. Washington State University entomologist David Crowder emphasizes the importance of preventing their expansion beyond quarantine areas.

The study indicates that the beetles would likely flourish in the dry, agriculture-rich southeastern part of the state, where they were first discovered three years ago. If they escape current quarantine zones, they could potentially spread across the region, from Yakima to the Tri-Cities and northwards to Moses Lake. While the Cascade Mountains act as a natural barrier, western Washington also offers suitable habitat for these pests.

Although Japanese beetles have already spread throughout much of the United States, they have only recently reached western states. They were first detected in Washington in a parking lot in Sunnyside in 2020, and trapping efforts have contained them mostly in that area. However, there has been one report of them just outside Seattle in 2023.

The success of quarantine zones has been evident, as guidelines prevent the movement of yard waste and agricultural outside the affected areas. However, human activity inadvertently contributes to their dispersal, as people may unknowingly transport these pests to new regions.

To tackle the issue, it is crucial to engage both the agriculture industry and residents in reporting sightings of Japanese beetles and taking appropriate measures. WSU research assistant professor Gengping Zhu emphasizes the challenge of detecting the beetles in their early life stages, making public involvement essential.

The study and control efforts aim to prevent the Japanese beetle from becoming an endemic problem in Washington. With climate change and increased human connectivity, ' spread will likely worsen, making coordinated and early identification efforts even more critical.

For more information on identifying Japanese beetles and preventing their spread, individuals can visit

Source: Washington State University

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