The Japanese beetle may spread throughout Washington state in the next 20 years, according to a study by Washington State University and the Washington State Department of Agriculture.
“The invasion of [the] Japanese beetle is of major concern as it feeds on over 300 plant species and has shown an ability to spread across landscapes,” the study abstract reads.
The iridescent, green-and-copper beetle, Popillia japonica, is a species that can cause “notable yield reductions” in crops, according to the Journal of Insect Science. Researchers recommended “quarantine and eradication” due to their potential to spread statewide.
The first beetles detected in Washington were found in 2020 in Sunnyside, between Yakima and Richland, according to the study. Two years later, the WSDA trapped more than 20,000 of the insects in Sunnyside and Grandview in south central Washington.
Currently, the beetles are mostly confined to areas with “highly suitable” habitats like dry, agriculture-rich parts of the state, although there has been one report from just outside of Seattle.
Researchers advocate the use of map-based predictions to limit the beetles’ spread.
The beetles first reached America’s East Coast in the early 20th century and have slowly been spreading west. They damage crops like fruit, corn and soybeans, along with flowers and ornamental plants, according to the Journal of Insect Science.
More than $460 million are spent annually to control larval and adult Japanese bettles, according to a U.S. Department of Agriculture report from 2015.
“Without its natural checks and balances, the Japanese beetle has become a serious plant pest and a threat to American agriculture,” the report said. “We must learn to ‘live with’ or manage this insect pest while attempting to minimize its impacts.”
