The Japanese beetle (Popillia japonica) is one of the most devastating pests in the United States. It typically feeds on more than 300 host plants including grape leaves. The beetle defoliates the leaf and leaves the marks which one can clearly see once it is gone. Gardeners know it all too well. The individual beetle doesn’t seem to damage the leaves but when they come in large numbers they do.
Japanese Beetle Facts
- Adult Japanese beetles reach a length of about 8 to 11 mm (1/3 to 1/2 inch) with the width measuring up to 5 – 7 mm.
- They are mainly recognized by their shiny green metallic as well as coppery-brown wings.
- Some part of the beetle’s abdomen is exposed as the wings don’t cover the entire body.
Distribution & Habitat
- The Japanese beetle occurs in Japan, United States, Russia, Portugal, China, and Canada. The beetle is widely distributed to many states of United States including Wisconsin, Mississippi River, Missouri, Oklahoma, Arkansas, Iowa, Nebraska, Minnesota, and Kansas.
- The beetle is not found in Florida.
- A female is likely to lay eggs in the soil but they favor habitats which are abundant in grasses. In grassy areas, the grubs readily develop.
Feeding Ecology & Diet
- Japanese beetles are likely to consume primary plants which include stone fruits as well as peaches, plums, maples, raspberry, blackberry, corn, asparagus, soybean, rhubarb, limes, grapes, roses, and elms.
- However they also eat some of the secondary plants such as poplars, rosemallows, chestnuts, willow, American mountain ash, birches, common sassafras, planes, buckeyes, turf grasses, and hollyhocks.
- In Virginia and Philadelphia, Japanese beetles seem to feed on grapes as early in summer as in June 1 to June 15. However in the New England they start eating grapes in July.
- They keep relying on grape leaves for as long as 30 – 45 days. Favored among these grape leaves are those that are all exposed to the sun. These leaves later fall when they are badly damaged.
Lifecycle & Development
- A female beetle lays 40 to 60 small white oval-shaped eggs in her entire life. The lifecycle of a Japanese beetle is about one year.
- Japanese beetle’s eggs hatch in about 10 – 14 days. The eggs measure about 1.5 mm in diameter.
- Females make a burrow of about 2 – 3 inches deep where it deposits eggs. Beetles that develop in the soil remain in the soil for about 10 months. These are white grubs. Grubs attain a full length (of about one inch) in August.
- White grubs mostly eat vegetable seedlings as well as roots of turfgrasses.
- The Japanese beetle’s habitat must receive enough rainfall or moist soil in order to prevent grubs from drying out. This explains why beetles fancy laying eggs in golf courses, irrigated canals, or in grassy areas. Japanese beetles are able to survive even in high rainfall or high moisture soil.
- They may even go 8 – 10 inches deep down if the temperature of the soil reaches 60 degree Fahrenheit.
- The pupae stage of a Japanese beetle occurs when the grub beetle begins to transform into a beetle. They are creamy to reddish brown in color.
- The average lifespan of an adult Japanese beetle is 30 – 50 days.