Destructive beetles multiplying rapidly in Tri-Cities. Why you should care

The number of invasive Japanese beetles trapped in Pasco and Kennewick is up significantly this year, but Washington state Department of Agriculture officials are hopeful that a new method of eradicating them will be successful.

“It is quite alarming, the population increase this year,” said Camilo Acosta, the department’s beetle eradication coordinator, in an update to the Franklin County Commission.

Japanese beetles feed on more than 300 plants and can devastate grape crops, strip roses and other garden plants of their leaves, and damage turf at homes, parks and golf courses.

Last year, the state caught 408 Japanese beetles in traps in Pasco, up from five in 2023. It also trapped a Japanese beetle in Kennewick, which was a first for the city.

So far this year, 2,061 beetles have been recovered from Pasco traps – a five-fold increase from 2024. In addition, 10 Japanese beetles have been collected from traps set up at nine places in Kennewick.

The Japanese beetles in Pasco have mostly been found from the Columbia River north to the Interstate 182 area and from North Road 68 east to North Oregon Avenue

The Japanese beetles trapped in Kennewick appear to be “strong flyers” that made it over the Columbia River from Pasco and began establishing populations, Acosta said.

In Kennewick, the beetles have been found in Columbia Park, with others found within a few blocks of West Kennewick Avenue to the east of Highway 395. One beetle was found in the vicinity of West Klamath Avenue and North Shepherd Street.

In Richland, one Japanese beetle was found in 2002 near Target, but no others. Agriculture officials concluded it likely was a stray that came into town with stock for a nearby plant nursery and was not able to mate.

The beetles emerge – usually from beneath lawns or in other soil – in the spring and feed throughout the summer. From fall to spring their larvae, or grubs, overwinter in the soil.

For the second year in a row the Department of Agriculture has treated soil with insecticide in the spring to kill Japanese beetle grubs before they emerge from the ground as adults.

In 2024, the state expanded the treatment area from 1 square mile to 8 square miles, including part of Columbia Park in Kennewick.

Treatment requires permission from private and public landowners, and the Department of Agriculture has had slightly higher cooperation on infested areas of the Tri-Cities than elsewhere, Acosta said.

In addition to homes, the infestation area includes a golf course, schools and parks, which the state had permission to treat.

Most Japanese beetles have been found in the Lower Yakima Valley since three beetles were discovered in Grandview in 2020.

Last year, 24,700 were found in Sunnyside, Grandview, Mabton and the far west side of Benton County, including the Prosser area.

New treatment method

The Washington state Department of Agriculture has started a treatment method to eradicate the beetles this year, using insecticide on shrubs and trees where traps have caught 50 or more of the beetles before moving efforts to areas where lower numbers of beetles were collected.

Other western states have not seen major drops in population until they started killing adults, Acosta said. However, he expects the effort in the Tri-Cities to require five to 10 years to eradicate the beetles.

The state expects to wrap up spraying of shrubs and trees Aug. 15. The Japanese beetles emerged early this year, with the number of adults caught peaking in early July. Traps for the beetles will continue to be checked until October.

The Department of Agriculture also is in talks with Pasco and Franklin County officials about the possibility to create a quarantine area in 2026 for yard debris that could harbor Japanese beetles. Residents in the quarantine area would need to take vegetative waste to a collection site in the quarantine area, under the proposal.

“We don’t want this beetle spreading more than it already has,” Acosta said.

The area where Japanese beetles have been trapped in Pasco and part of Kennewick are slowly expanding as their population spreads.

But state officials are concerned that Japanese beetles could spread farther distances through yard debris or other material, such as potted plants, to other cities and counties.

They suspect that people unknowingly transported the beetles in vegetation or waste from the Lower Yakima Valley to start the infestation in Pasco.

What to look for

The beetles, native to Japan and southeast Asia, are metallic green and copper and have little tufts of white hair on their sides as adults.

Roses are their favorite host plants, but they eat grapes, hops, sweet corn, raspberries and about 300 other plants, turning them into skeletons as they consume the foliage, flowers or fruit.

They lay eggs primarily in lawns, and the developing larvae, or grubs, eat the roots and can destroy grass in yards, parks and golf courses. In addition to hanging yellow and green traps in the Tri-Cities, the Washington state Department of Agriculture is urging Tri-Cities area residents to keep an eye out for Japanese beetles and report them when spotted.

If you suspect you have seen Japanese beetles, take a photo and report the sighting at agr.wa.gov/beetles or email the photo along with the location of the sighting to pest@agr.wa.gov. If you find a Japanese beetle on your property, it can be killed by putting it in soapy water.

Washington State University Extension also has information on treatment options for infestations of Japanese beetles, both as grubs and adults.