Japanese Beetle in Idaho

The Japanese beetle (JB), Popillia japonica, is a highly destructive plant pest that can be difficult and expensive to manage. Feeding on grass roots, JB grubs, the immature stage of the insect, damage lawns, golf courses, parks and pastures. JB adults consume the foliage, flowers and fruits of more than 300 different ornamental and agricultural plants.

First found in the US in 1916 in a New Jersey nursery, JB has since spread throughout most states east of the Mississippi River. Partial infestations also occur in states such as Arkansas, Iowa, Kansas, Minnesota, Missouri and Oklahoma. Infestations in western states have been eradicated before the insect became established.

In 1990 the Idaho State Department of Agriculture (ISDA) began monitoring the state for Japanese beetle (JB) using pheromone-baited traps. Each year ISDA deploys approximately 340 traps in high risk sites like nurseries and airports. On rare occasions (1992, 1997 and 2011) ISDA trapped single specimens at nurseries, most likely hitchhikers on nursery stock from other states. Locations of beetle capture were treated with pesticide and JB never established in Idaho.

During the summer of 2012 ISDA traps collected a total of 61 Japanese beetles: 4 near a nursery in Kootenai County, 1 near a nursery in Bannock County and 56 in Ada County. ISDA immediately placed several delimiting traps around the two positive locations in the Boise area. Most of the beetles caught in the Boise area were trapped in a residential area in the eastern part of the city.

In 2012 ISDA determined the source of the Japanese beetles found in Idaho may have come from a single Midwestern commercial nursery business that shipped nursery stock to Idaho and other nearby states.

In 2013, with the number of traps increased statewide to 1,553, beetles were collected nowhere except in east Boise, however, numbers there increased to 3,058 individuals. Most were in a residential area on the city’s east side.

95 residential properties and 11 city parks were treated with granular and liquid insecticides in an attempt to eradicate JB grubs and adults.

In 2014 ISDA increased the number of survey traps to 2,947 to more accurately determine where JB populations were located and to aid in effective control efforts. Trap data from 2014 indicated that the 2013 insecticide treatments appeared to have a positive effect, with beetle numbers down overall about 60% - 1,283 JB were captured in the traps during 2014.

Where the first 95 residences were treated, during 2013 traps captured 1,930 JB and in 2014 only 91 beetles were found – a 95% reduction.

Based on these results treatment was again carried out however, the treatment area was expanded to include 500 residential/commercial properties where beetles were caught plus 14 city parks.

In 2015, JB trap data again indicated another significant decrease in JB population. Similar to 2013/2014, with regular survey traps throughout the state, the only JB captured were in Boise, and this year's total dropped to 365 - an 81% reduction from 2014. The area containing the original 95 treated residences produced only 18 JB catches. Parks treated twice exhibited a decrease from 527 to 18 JB.

With a goal of total JB eradication, 2015 treatments were stepped up even more with approximately 1,900 residential/commercial properties, plus parks, taking part in the program.

In 2016 only 128 JB were found. Many locations where JB were captured during 2013-2015 appeared to be beetle-free in 2016 and in places they were found, JB density was dramatically reduced. The same insecticide-treatment program used in 2014/2015 was conducted in 2016, however, total treatment area was reduced 40% from 550 acres (2015) to 340 acres (2016) in response to a diminished JB population.

With a continual decline in the number of JB captures each year, 2017 only had 19 JB catches. Areas chosen for treatment were based on the location of beetle captures during the previous year. As JB populations decreased and areas infested began to shrink, treatment areas also were reduced, with only 400 residential/commercial properties and 3 parks requiring treatment in 2017 totaling 60 acres.

In 2018, ISDA saw another decrease with only 4 JB catches in the Boise area. ISDA also had a new JB find in Pocatello, Bannock County, where a single JB was caught. ISDA planned delimitation trapping in Pocatello around the positive JB site and continuing with the Boise delimitation trapping.

Treatments for Boise in 2018 included 400 residential/commercial properties and 3 parks requiring treatment totaling 40 acres.

In 2019 ISDA continued with delimitation trapping in the Boise area. ISDA reduced the number of Boise delimit traps to 682 and in 2019 Boise had no positive traps. Because of the single JB catch in Pocatello in 2018, ISDA added 29 delimit traps around the positive site and 4 beetles were caught in Pocatello during 2019.

No Idaho treatments were planned or carried out in 2019.

For 2020 delimitation trapping continued in Boise and Pocatello. Boise delimit traps were reduced to 449. Pocatello traps were increased from 29 traps in 2019 to 104 in 2020. The only positive traps this year were located in Pocatello, Bannock County. Number of beetles captured was 7.

There were no Idaho treatments planned or carried out in 2020.

In 2021 delimitation trapping continued in Boise (250 traps) and Pocatello (104 traps). Boise had no JB catches and in Pocatello 11 JB were caught at five separate sites. Also, ISDA had a new single JB catch in a cemetery in Caldwell, Canyon County.

No 2021 treatments were planned or carried out in Boise, however, two parks in Pocatello (where most of the JB were captured in 2020) received turf pesticide treatments. Plans for 2022 included follow-up trapping (reduced in Boise and Pocatello and increased in Caldwell) and a second treatment in one of the parks in Pocatello.

In 2022 Boise JB was considered eradicated and the area put back into JB detection survey mode. The Boise eradication plan is currently the largest, successful eradication of JB ever documented in the United States.

Delimit trapping continued in Pocatello, however, number of traps was decreased to 49. A total of 8 JB were captured in two traps - both in one park - which was treated for a second year.

During the 2022 field season, 49 delimit traps were initially set up in Caldwell, centered around the cemetery harboring the 2021 catch. When JB were found in traps south of the cemetery 33 additional traps were added to expand the survey area. Between July and September, 77 JB were collected in the traps, defining an established infestation.

In 2023 ISDA continued with their state wide detection survey for JB. The delimit survey in the Pocatello area continued with 52 delimit traps and 4 JB beetles were caught. Treatments were performed in the parks where the traps were positive in Pocatello. The Caldwell delimit traps increase to 399 traps centered around the positive locations uncovered in the area in 2022. In 2023, 260 JB beetles were caught in the Caldwell area. ISDA treated around 232 acres in Caldwell. Also during the 2023 trapping season one JB beetle was caught in the Boise area. ISDA will plan to run delimit traps in the area in Boise to ensure there is not a larger population.

Treatment plans for 2024 are being formulated for both the Pocatello and Caldwell areas.

In 2024 ISDA continued with their state wide detection survey for JB. The delimit survey in the Pocatello area continued with 52 delimit traps and 4 JB beetles were caught. Treatments were performed in the parks where the traps were positive in Pocatello. The Caldwell delimit traps increase to traps centered around the positive locations uncovered in the area in 2022. In 2023, 260 JB beetles were caught in the Caldwell area. ISDA treated around 232 acres in Caldwell. Also during the 2023 trapping season one JB beetle was caught in the Boise area. ISDA will plan to run delimit traps in the area in Boise to ensure there is not a larger population.