Idaho is winning its fight against the Japanese beetle in Boise

Lloyd Knight, administrator of the division of plant industries with Idaho Department of Agriculture, checks a Japanese beetle trap in 2015.
Lloyd Knight, administrator of the division of plant industries with Idaho Department of Agriculture, checks a Japanese beetle trap in 2015.

Update, Aug. 30, 2016:

Idaho is gradually winning its multiyear campaign against Japanese beetles in Boise.

After the number of the metallic green beetles caught in traps in the city exploded from 61 in 2012 to 3,038 in 2013, the Idaho Department of Agriculture ramped up its pesticide program, treating about 1,900 sites in 2015.

As a result, 365 beetles were trapped in yellow-and-green traps hung at selected points throughout the city in 2015. The traps have caught just 127 caught so far in 2016. 

The traps are used primarily to measure the presence of beetles, not to kill them. For that, the state applies pesticides. The department's beetle team cut the number of treatment sites in half and plans to reduce further next year.

After hatching in July, the beetles live in soil for 10 months as grubs, eating roots, killing grass and plants, and damaging yards, golf courses and parks. They take to the air the following June, and they eat more than 300 kinds of trees and plants, including yard and garden plants as well as cash crops such as corn and fruit trees. That is why the state has been spending money to eradicate them.

The story below was published in August 2015 under the headline, "Inside Boise’s battle with the Japanese beetle."


Paul Castrovillo first started chasing the Japanese beetle in third or fourth grade in the mid-1960s, catching and collecting them on rose bushes in his New Jersey backyard along with butterflies and whatever other bugs were around.

He researched them, learning about their diet and life cycle. He occasionally roasted one with his magnifying glass.

The Japanese beetle was not then the top insect threat in Idaho, as it is today. But it had already infested most of the eastern quarter of the U.S., chewing through grass, plants and crops as its population skyrocketed.

The metallic green beetles were not a problem in Idaho until 2012, when 61 were collected in traps set by the Idaho Department of Agriculture, all in Boise’s Warm Springs neighborhood. The state set more traps and found more than 3,000 beetles the next summer.

Not wanting to become another New Jersey, Idaho looked for a bug expert to battle the beetles. They found Castrovillo, who, among other jobs, had worked in Micron’s research and development department for 19 years after graduating from the University of Idaho with a Ph.D. in entomology in 1982.

He had the degrees for the job, as well as experience collecting, identifying and archiving more than 30,000 specimens for The College of Idaho’s natural history museum in Caldwell. He did that on weekends and vacation days over 20 years as he set traps and swung butterfly nets.

Castrovillo told the department officials he had waited more than 30 years for such an opportunity.

“I’ve been doing this out of sheer love,” Castrovillo said. “If you’re looking for somebody to do this as an 8-to-5 job. I’d love to have it.”

Most kids go through a phase where they take interest in the fantastic, often alien-like bugs in their backyard, Castrovillo says. “Every once in a while, you get a kid like me, who 60 years later hasn’t grown out of it.”

Castrovillo was always partial to moths and butterflies, such as the ones pinned in specimen boxes in his office. He still hopes to find a rock crawler, a rare bug living in cold, high-elevation habitats that some say will die if exposed to the heat of a human hand. But he remembered the Japanese beetle well.

“It’s kind of like seeing an old friend,” he said.

Today, Castrovillo works near the epicenter of the beetle outbreak in the department’s office on Old Penitentiary Road, off Warm Springs Avenue. Two small boxes full of shiny specimens pinned in neat rows decorate his desk. Maps of Boise marking many of the 2,500 traps set in the city decorate the walls.

Castrovillo and his team are in the third year of applying pesticides to select public and private properties in areas showing the highest Japanese beetle concentrations. The treatments, which take a year to take effect, have been successful, knocking the beetle count to 329 across the city this summer, on pace for a 72 percent reduction from last summer and 91 percent since 2013.

The traps measure the presence and density of Japanese beetle populations in neighborhoods, but they don’t attract enough to eradicate the pest.

The state budgeted $400,000 in each of the past two years for the Japanese beetle eradication program, he said. All other insect surveys, including for gypsy moth and apple maggot, cost about $40,000 annually.

Castrovillo talks to property owners about how the pesticide program works. Some are hesitant to give permission to treat their yards, saying they dislike the idea of chemicals in their soil and around pets, children and other plants. Castrovillo explains that the two chemicals his team uses, Acelepryn and Imidacloprid, kill immature grass-eating insects such as Japanese beetles and billbugs but are not toxic enough to affect larger humans, pets or insects. Yards are treated with granules of the chemical rather than a spray to avoid wind carrying the treatment onto other properties.

The goal, Castrovillo said, is to wipe out Japanese beetles over seven years, the same time it took to eradicate a similar population in Orem, Utah, a few years ago. If successful, the program would avoid a beetle population that would lead to residents applying their own, less-selective pesticides in perpetuity.

“I’m sure you know neighbors who think if spraying once is good, three times a year is even better,” he said. “That’s turned some people who didn’t want chemicals on their yard to turn to our side.”

The first 95 properties where owners consented to treatments in 2013 have seen the number of Japanese beetles collected fall from 1,930 to 91 in 2014, a 95 percent reduction. Eight department employees balance working on the eradication program with other tasks, and four part-time employees work seasonally. More than 2,000 Boise properties were treated in the last year.

Even if the program decimates the Japanese beetle population in Boise, a single hitchhiking bug could spread the problem to crop fields or cities elsewhere, Castrovillo said.

“We believe it came from nursery stock from the east, probably in a truck,” Castrovillo said. “If it can survive the drive from Minnesota to Idaho, it can survive the drive from Boise to Moscow or Twin Falls a lot easier.”



Adult Japanese beetles are about a half-inch long and have coppery wing covers and metallic green bodies. After hatching in July, they live in soil for 10 months as grubs, eating roots, killing grass and plants, and damaging yards, golf courses and parks. When mature, they take to the air in June and eat more than 300 kinds of trees and plants, including yard and garden plants as well as cash crops such as corn and fruit trees. "It's like the ultimate pest because it feeds on so many different things at all stages of its life, " Castrovillo said.


To learn more about Japanese beetles, the eradication program or to request treatment for your property, visit the Idaho Department of Agriculture's Japanese beetle website.


The Idaho Department of Agriculture keeps its eye on several insects slowly migrating from the East Coast. Bugs it hopes to keep out of Idaho include:

Gypsy moth: The moth's caterpillars devour shrubs and trees. The moth has moved slowly west since first being discovered in the U.S. in Massachusetts in 1869. Idaho Department of Agriculture has found several moths over the years but never in consecutive years at the same location.

Asian longhorned beetle: This beetle infests parts of Massachusettts, New Jersy, New York and Ohio, where it threatens forests. The pest has never been found in Idaho but remains a concern because of the damage it can do to hardwood trees.

Emerald ash borer: The bright insect has destroyed tens of millions of ash trees in 25 states in the Midwest and Northeast.

Spotted wing drosophila: First found in California in 2008, the small, fruit-eating fly has been found elsewhere around the country, but so far not in Idaho.

Source: U.S. Department of Agriculture