As its name indicates, the Japanese beetle originates from Japan. In Japan, the beetle is not a serious pest because a number of insect parasites and predators feed on the beetles. However these natural enemies do not exist in the U.S., so the beetle has been able to spread across the eastern half of the U.S. Intense monitoring and regulation has, thus far, kept the beetle species from becoming established west of the Mississippi.


 

Japanese Beetle and Grub Identification

The adult beetle is:

• is just under 1/2 inch long
• has a shiny, metallic-green body with bronze-colored outer wings
• has six small tufts of white hair along the sides and back of its body under the edges of its wings.
• male is usually slightly smaller than the female

 

The beetle grubs, or larvae:

• are about 1 inch long
• are whitish in color
• lies with its body in a curled C-like position.

 

Pupae are:

• off-white to tan in color
• egg-shaped with external legs.

 

Japanese Beetles and the Four Seasons

The life cycle of the Japanese beetle can be charted by the changing of the seasons:

• Winter – Japanese beetle grubs lie dormant deep in the soil through the cold winter months
• Early Spring – the grubs "awaken" begin feeding on roots
• Late spring – after feeding, the grub pupates to develop into an adult beetle
• Early summer – beetles emerge and begin feeding on plants and leaves
• Mid- to late summer – beetles feed, mate, lay eggs beneath the soil. A female can lay up to 600 eggs in a single season.

• Late summer to early fall –grubs hatch and feed heavily on underground roots
• Late fall - grubs burrow down into the soil preparing for winter dormancy and beginning the cycle anew.

 

Japanese Beetle Damage and Destruction

Many insects are destructive in only a single stage of their development. For example, many stored food insects feed only during their larval stages, while mosquitoes bite only as adults (and only the females!) Japanese beetles are an exception, as the larva "grub" stages lived underground and feed on plant roots, while the adults fly and crawl above ground, feeding on the leaves and fruit of the plants.

The USDA estimates that turf-grass losses attributable to the larval stage alone are $234 million per year—$78 million for control costs and an additional $156 million for replacement of damaged turf.

 

Do You Have a Japanese Beetle Problem?

Japanese beetles can fly long distances, so you may see some on your property that actually came from elsewhere. To determine if you have a problem on your property, USDA recommends that you survey for adults and grubs.

1. Survey your property for adult beetles. This can be done through the use of Japanese beetle traps which lure beetles in. To determine the extent of the infestation, place the trap where adult beetles are seen. If the trap fills in a day – you probably have a problem; if a week goes by and the trap in barely filled, there is probably not a concern.
2. Survey your property for grubs. This is best done in late spring or late summer. Take several random samples around the lawn – dig a square hole 8 x 8 x 3 inches deep; turn over the sod, then count the number of grubs in the grass roots and the soil in the hole. (When putting the sod back in place, water it to help with its recovery.) If more than 5 grubs were found in any single section (or 10 per square foot), treatment is recommended.

 

For control recommendations, see How to Control Japanese Beetles and Grubs.