SIZE: Adult Japanese beetles are between one-third and one-half of an inch in length. Females are typically larger than males. Larvae are about 1 inch in length.
COLOR: These beetles have metallic green bodies with copper-colored wings. Larvae are white and C-shaped with light brown heads and grayish bottom tips.
BEHAVIOR: The Japanese beetle is an extremely destructive pest, causing severe damage to turf, landscape and ornamental plants. It can also cause damage to fruits, gardens and other crops. The life cycle of this pest takes about a year to complete. Adults emerge around June or July and immediately begin to feed, mate and lay eggs. An average adult lifespan is between 30 and 45 days.
Peak feeding times occur at full sun. Damage to leaves and plants emit an odor that causes beetles to aggregate. The beetles also release a pheromone that encourages aggregation and mating. As the sun sets, the production of this pheromone is reduced. Females take this time to burrow about 2 to 3 inches into the soil and lay eggs. A single female can lay a total of 40 to 60 eggs during her lifetime. These eggs develop into white grubs beneath the soil, and become full-size grubs by the end of August. Grubs remain beneath the soil for the next 10 months or so, feeding on the roots of turfgrass and vegetable seedlings.
As a result of their eating habits, adult Japanese beetles and their immature offspring cause different types of damage. Adults destroy the leaves and flower bulbs of living plants. Grubs corrupt roots and inhibit the growth of grass and other plants and vegetables. They are particularly destructive to home lawns, golf courses, parks and cemeteries.
Native to the country of its namesake, the Japanese beetle was first discovered in South New Jersey. It is now widespread throughout the United States. This invasive species thrives in areas with steady precipitation and soils that have an average temperature between 64 and 82 degrees Fahrenheit.
TIPS FOR CONTROL:
Grubs and adults also require different methods of control. Timing treatments when targeting grubs is important. Applying ground treatment from mid-July to early September can reduce the number of grubs living beneath the soil, although treatment becomes less effective as the grubs grow. When targeting adult Japanese beetles, treatments should be applied to plants and surrounding foliage.
Adult beetles may also be managed by hand removal, especially in areas where the population of Japanese beetle is small. Making careful plant selections before starting a garden can be an effective prevention method. Grass that is already dying as a result of beetle damage may be too damaged to save. To prevent severe damage such as this, hire a pest management professional.