Potential distribution and spread of Japanese beetle in Washington State

The Japanese beetle, Popillia japonica (Newman, 1841) (Coleoptera: Scarabaeidae), was first detected in southern Washington State in 2020. Widespread trapping efforts ensued, and over 23,000 individuals were collected in both 2021 and 2022 in this region known for specialty crop production. The invasion of Japanese beetle is of major concern as it feeds on over 300 plant species and has shown an ability to spread across landscapes. Here, we created a habitat suitability model for Japanese beetle in Washington and used dispersal models to forecast invasion scenarios. Our models predict that the area of current establishment occurs in a region with highly suitable habitat. Moreover, vast areas of habitat that are likely highly suitable for Japanese beetle occur in coastal areas of western Washington, with medium to highly suitable habitat in central and eastern Washington. Dispersal models suggested that the beetle could spread throughout Washington within 20 years without management, which justifies quarantine and eradication measures. Timely map-based predictions can be useful tools to guide management of invasive species while also increasing citizen engagement to invaders.