The Japanese beetle, a most destructive garden pest, devours just about everything in its path, including well-tended trees and shrubs. The damage it causes is disheartening, but you can arm yourself with knowledge and keep this pest under control in your yard.
A Foreign Menace
As its name suggests, the Japanese beetle is a native of Japan, where it has natural enemies that keep it in check. The U.S. Department of Agriculture reports that the pest was first sighted in the United States at a southern New Jersey nursery in 1916.1 Because natural enemies of the beetle don't exist in the U.S., the pest has wreaked havoc on plants since its arrival. It took only four years for the pest to cause severe damage in 22 states after making its way to America. Monitoring and rigid regulations have helped prevent or slow the pest's establishment in the remaining states.1
Beautiful but Destructive
At a little less than 1/2 inch long, the Japanese beetle is hardly imposing. In fact, it might be considered somewhat attractive. The oval-shaped insect is metallic green with bronze-colored wing covers and dark legs. A telltale characteristic that distinguishes the Japanese beetle from other beetle types is the series of small, white tufts of hair located under the wing covers along each side of its body and on its hind end.
In the spring or early summer, adult female beetles lay eggs in soil. Those eggs hatch and become unattractive larvae known as grubs. The white, c-shaped grubs have dark heads and feed on plant roots, often causing severe damage. The larvae stay in the soil until the following spring, when they pupate and become adults.
The Japanese beetle has a voracious appetite that makes it especially destructive. The adult beetle feeds on about 300 species of plants — roses, shrubs, vines, ornamental and fruit trees, and vegetable crops — devouring foliage, flowers, tree and shrub buds, and fruit.2
Because of its distinctive feeding pattern, Japanese beetle damage to trees and shrubs is easy to spot. The pests dine on the soft tissue between leaf veins, leaving leaves skeletonized and lace-like. Flower petals become ragged after beetles feed on them; trees hit hard by beetle feeding may appear as though scorched by fire.2
Japanese beetles are most active on warm, sunny days and like to feed in direct sun in groups. The adult beetles are able to fly, which allows them to move easily and quickly throughout your landscape and join others. They begin eating at the top of plants and work their way down.3