Insects & Other Arthropods
Japanese Beetle Repeatedly Eradicated from California
Adult Japanese beetles are shiny with a green head and thorax and wing covers that are mostly coppery brown. Adults are broadly oval and 1/3 to 1/2 inch long. The antennae at the tip have several fingerlike swellings (lamellae). Twelve discrete tufts of short white hairs occur around the margin of the abdomen. The oval to spherical white eggs are about 1/16 inch long and occur in soil.
The larvae and those of other species in the insect family Scarabaeidae are called white grubs. Larvae are creamy white to translucent and have scattered long brown hairs and short bristles. Fecal matter in the hindgut is visible through the body covering and gives their rear end a dark to gray coloration. Larvae occur in soil and grow to about 1 inch long. When observed white grubs commonly have a C-shaped posture.
Pupae occur in late winter or spring in a soil cell formed by the last instar. The pupa is about 1/2 inch long and oblong. It initially is creamy white then darkens to brownish and green as it ages.
Adults and larvae of various other beetles, mostly other Scarabaeidae, can be confused with those of Japanese beetle. The pattern of short bristles on the underside of the last abdominal segment (hind end, or raster) distinguish larvae of Japanese beetle from similar-looking species of white grubs. Some of the bristles on Japanese beetle form a distinctive V shape just in front of the anal slit. Other species of white grubs lack this V pattern of bristles.
When adults are viewed from above the wing covers of Japanese beetle do not completely cover the abdomen. This exposes 12 discrete patches of short, white hairs around the margins of the abdomen. These 12 clumps of hairs distinguish Japanese beetle from adults of similar-looking beetles.
Adults of other beetles that are coppery brown, green, or both are sometimes mistaken for Japanese beetles. But none of these species have 12 discrete patches of short, white hairs projecting around the abdominal margin as do Japanese beetles. Adult lookalikes include
Japanese beetle develops through four life stages: egg, larva, pupa, and adult. The adults are present from late spring to summer. Based on its biology in the Eastern United States the mated females tunnel in soil, most commonly in turfgrass. They lay one to several eggs near plant roots. Females periodically emerge and mate and repeatedly burrow into soil to lay a few eggs at a time for a total of about 40 to 60 eggs per female.
Eggs hatch in about 10 to 14 days. The young larvae seek roots on which they chew and feed. Most of the life cycle (about 10 months) is spent as larvae underground. Larvae develop through three increasingly larger instars that feed during summer and fall and again in the spring before they pupate into adults.
Japanese beetle's biology in California is not definitely known because it does not regularly occur here. In the Eastern United States it has 1 generation per year. In Northern Japan where the beetle is native it takes 2 years to complete 1 generation.
Japanese beetles chew and feed on more than 300 species of fruit tree and vine crops, landscape trees and shrubs, herbaceous ornamentals, and turfgrasses. For example members of the families rose (Rosaceae), grass (Poaceae), and legume (Fabaceae) are common hosts.
Adult Japanese beetles feed mostly on blossoms and foliage. They also feed on fruit that is injured or over ripe. Adults commonly congregate in groups on the foliage of host plants to feed and mate. The larvae chew and feed underground on roots, especially on turfgrasses. In the Eastern United States approximately $450 million per year is spent to manage this serious pest.
Where Japanese beetle is established in the Eastern United States it is managed with broad-spectrum insecticides and more selective microbial insecticides such as Bacillus thuringiensis galleriae and Heterorhabditis species entomopathogenic nematodes. Cultural controls include choosing species that are resistant to feeding by Japanese beetle, removing fruit that drops or is injured, and harvesting before it becomes overly ripe. Modifying fertilization, irrigation, and mowing are used for turfgrass.
Traps are available for selectively attracting and capturing the adults. But traps have not been shown to provide control of this pest. It appears that placing one or several traps in a landscape can actually increase the number of beetles feeding on leaves and grass roots because only a portion of the attracted beetles are captured in the traps.
Since it was introduced into the Eastern United States in about 1916 this serious pest has not become established in California. The California Department of Food and Agriculture (CDFA) throughout the state maintains traps for detecting Japanese beetle. For example in 2019 CDFA caught Japanese beetles near airports in Burbank, Los Angeles, Ontario, Sacramento, San Diego, Santa Ana, and Stockton. Where the beetle has been found feeding in California it has been successfully eradicated, preventing this pest's damage and the ongoing insecticide application and other management that occur where it is established.
If you find suspected Japanese beetles in California, collect individuals if possible. Place them in alcohol or the freezer to kill them. Do not move off the property any live beetles suspected of being this pest. Report any finding of suspected Japanese beetles to the local office of the county agricultural commissioner or telephone the CDFA Pest Hotline at 800-491-1899.