Facts, Identification & Control
Adult Japanese beetles can be easily identified by their coloring. The Japanese beetle has a metallic green body with copper-brown wing covers. Adults appear from the ground and begin feeding on plants in the early summer. The peak of their activity lasts from late June through August or September when they will begin to die off due to temperature and climate. Japanese beetles live for up to two months during their adult life form.
Behavior, Diet & Habits
Japanese beetles are commonly known to cause a multitude of damage to a variety of plants including vegetable crops, flowering plants and ornamental shrubs such as rose bushes. They are attracted to the leaves produced by these types of plants. The Japanese beetle is believed to have originated in the country of Japan and was first noticed in the eastern United States in the New Jersey area in the early 1900s. The beetles were most likely introduced in the United States through commerce, and they were able to thrive and survive due largely to the eastern U.S. being able to provide a favorable climate, large areas of grass for developing grubs, hundreds of species of plants on which adults could feed and no effective natural enemies. The beetle feeds on a wide variety of plants and crops while the larvae or grubs, will feed on a variety of roots of ornamental trees, shrubs, garden plants and grass.
The feeding habits of Japanese beetles are what make them such a nuisance. They are opportunistic feeders and have been documented to feed on over 300 types of plants and crops. They also like to feed in groups, which causes them to do damage to a wide area if the food source that attracts them is available. The beetles are most active on warm, sunny days, and prefer plants that are in direct sunlight. Adults feed on the leaves and flowers of the food source. This gives the leaf a “skeletonized” appearance. Adult Japanese beetles are very transient and can infest new areas from several miles away whether it is from wind shift or introduction or food source availability. Typically they stay close to the areas that have the most plentiful supply of plant species that fit their feeding habits so that they can breed and lay eggs.
Adults dig their way out of the soil and mate in the summer. Eggs are laid by the female in short burrows they dig in the soil. She can lay between 40 to 60 eggs in her life. The larvae, called grubs, feed on roots in the soil and will pass the winter in a dormant state. In spring, they resume feeding and ultimately pupate into adults by the summer.
Signs of a Japanese Beetle Infestation
Homeowners often first notice Japaneses beetles when they see the skeletonizing of outdoors plants. Upon closer inspection of the plant, the adult beetles are easily seen as they feed on the plants. The adults also are active fliers and can be observed flying around the yard and plants.
From an extermination standpoint, it is important to recognize that both the adults and grubs can cause damage. Therefore a combination of cultural, mechanical and chemical controls should be used. Since Japanese beetles are capable of traveling from nearby areas or neighboring plants, control measures of the different life stages must be taken into consideration to eliminate the infestation. Control of the grub or larval stage requires properly timed applications of a soil insecticide to infested areas.
Cultural and physical controls would consist of habitat modification (planting plants that are less attractive to Japanese beetle adults) and physical removal of plants and/or the adult beetles by shaking them off early in the morning when the insects are sluggish. The beetles may be killed by shaking them into a bucket of soapy water.
Mechanical controls are applied through the use of traps with pheromone lures; however this will not correct any issues with grub infestations and can attract more beetles to the area.
Chemical control consists of using products labeled for use against adult Japanese beetles.