Ag department wages war on invasive beetle

By Sean Ellis

Idaho Farm Bureau Federation

POCATELLO – It may seem at times that the Idaho ag department is playing whack-a-mole with the Japanese beetle.

The beetle, a non-native invasive pest that attacks a wide variety of crops, has popped up in various spots in Idaho over the years.

Because it is a major threat to the state’s agricultural industry, the Idaho State Department of Agriculture surveys for the pest and whacks it down when it appears.

“We’ve been on a mission, if you will, for a couple of decades now to be on the lookout to make sure it does not make its way to becoming part of Idaho and another insect our growers have to fight with,” says Andrea Thompson, section manager of ISDA’s plant industries division.

The beetle is a highly destructive plant pest that feeds on more than 300 different agricultural and ornamental plants.

According to a recent University of Idaho study, agriculture accounts for one in every nine jobs in the state, 17% of total sales and 13% of total gross state product.

The ISDA has chased the pest wherever it pops up in Idaho and ensured it doesn’t gain a permanent presence here.

“We are kind of on the chase just trying to make sure that this pest that obviously can find a way to make it here doesn’t get a foothold in Idaho,” Thompson says.

The beetle has of late made appearances in Caldwell and Pocatello. The ISDA has undertaken a major eradication effort in Caldwell and is keeping a close eye on the pest’s presence in Pocatello and also trying to eradicate it there.

The ISDA requests permission from property owners in select Caldwell and Pocatello neighborhoods to conduct free treatments aimed at eradicating the Japanese beetle. 

Canyon County, where Caldwell is located, is a particular concern because of its proximity to an extensive amount of farmland. The county not only has the most farms in the state – 2,113 – it’s also one of the top seed-producing areas in the world and the center of Idaho’s $500 million seed industry.

Pocatello in Bannock County is not surrounded by as much prime farmland as Caldwell is, but Thompson says ISDA is also paying close attention to the beetle in that city because it doesn’t want it to even gain a small foothold in Idaho.

The department does have a good track record when it comes to fighting the beetle.

After dozens of Japanese beetles were detected in Boise in 2012 – the number of beetles detected in the Boise infestation exploded from 56 in year one to more than 3,000 in year two – the ISDA undertook a major eradication effort that resulted in the pest not being detected in Boise the past several years.

It was the largest documented Japanese beetle eradication in U.S. history, according to Thompson.

The ISDA is using the same type of template to go after the beetle in Caldwell and Pocatello.

In Caldwell, the beetle was first discovered in 2021 and then it expanded to become an infestation. The department responded aggressively and started treating for it in 2023 and 2024.

The pest’s population in Caldwell peaked in 2023 at 260 and then went down to 132 in 2024.

“It’s giving us every indication that that treatment is effective in cutting that population down and we’re on the same curve as the successful Boise eradication,” Thompson says.

The beetle’s numbers in Pocatello have been relatively small since it was detected there in 2021 and the department was able to isolate the population last year. As a result, the ISDA will have a more defined treatment area this year.

“We’re going to be more aggressive about that treatment area and increase the number of survey traps that we have there to make sure we’re not missing any other infestations,” Thompson says. “But we feel like we’ve got our thumb on it now and able to get that treatment honed in.”

The beetle, native to Japan, was first detected in the U.S. in 1916 and is now found in most states east of the Mississippi River.

Idaho does have preventative controls designed to stop the introduction of Japanese beetles into Idaho from infested states in the East. But it still does get here.

“It’s not foolproof,” Thompson says of Idaho’s protocols for stopping the beetle getting here. “It has a way of moving. It also does have the ability to hitchhike on aircraft and other means.”

Adult Japanese beetles are about a half-inch long and have metallic green bodies and coppery wing covers.

Adult beetles can leave holes in plants and skeletonize leaves.

The beetle has an appetite that extends to more than 300 species of plants, including some of Idaho’s top crops.

Thompson says ISDA has received excellent cooperation from residents, cities and the ag industry itself in its war against the beetle.

“Without the support and participation from the public and people that are in these infestation areas, our city partners and the ag industry, this success would not be possible,” she says.

The ag industry is very supportive of the department’s efforts, Thompson says. That’s due to the potential devastation the beetle can cause.

“The ag industry understands what it would mean to let this go,” she says.

Besides causing decreased production, the beetle’s permanent presence, if that ever happened, would mean increased pesticide use. There’s also the potential of losing markets that could impose quarantine restrictions.

“We really encourage everyone within the treatment zones to help protect Idaho agriculture,” Thompson says. “If they’re not within the treatment zone, just be on the lookout and report anything that would even seem close to being a Japanese beetle to ISDA.”

For more information about the pest, contact Thompson at (208) 332-8620 or by email at Andrea.Thompson@isda.idaho.gov.