A native of Japan and China, where it is not an important pest, the Asiatic garden beetle (Maladera castanea) was first discovered in the United States in New Jersey in 1922. Asiatic garden beetle grubs feed off the roots of grasses and weeds in early spring. Adult beetles attack many different vegetable, herb, fruit, and ornamental plants, feeding mostly at night where they strip, shred, and notch the foliage of their hosts. Asiatic garden beetle damage is especially prevalent around the leaf margins.
The Asiatic garden beetle is a small, velvety, cinnamon-brown, beetle, 3/8 inch long, and about the size and shape of a coffee bean. The female lay its eggs in the soil in clusters of up to 20, held together by a gelatinous material. The Asiatic garden beetle larva is a C-shaped white grub, with a brown head, six legs, a V-shaped anal opening, and a single transverse row of curved spines on the underside of the last segment. Mature grubs are about ¾ inch long.
The Asiatic garden beetle overwinters in the soil as a small grub feeding off the roots of grasses and weeds in early spring. The larva pupates in late May and June, emerging as an adult in late June and July. Adult beetles are attracted to light and may congregate in great numbers on windows, screen doors - wherever there is bright light. The females burrow into the soil to lay their eggs, which hatch in about two weeks. Though the Asiatic garden beetle has only one generation per year, adults may remain actively feeding throughout summer.
- Cultural Practices
- Handpicking: Handpick beetles at night using a flashlight or a light trap. When disturbed, Asiatic garden beetles instinctively drop downward, so using a broad bowl of soapy water to collect beetles feeding on plants may be a useful tool.
- Barriers: Spun-bonded fabric row covers may protect herb and vegetable planting beds against the predations of adult Asiatic garden beetle, unless larvae have overwintered in weedy garden soil.
- Sanitation: Prevent over-wintering by cleaning up your garden in fall, tilling under, or composting all weeds and plant debris.
- Monitoring - Monitor for the presence of Asiatic garden beetles by visiting your garden at night and shining a bright light down onto the soil. Adult beetles will be attracted by the light.
- Chemical Control - Chemical control is rarely needed for Asiatic garden beetle grubs on New Hampshire lawns. However, a number of insecticides are registered to control adult Asiatic garden beetles feeding on plant foliage. Read and follow all label directions carefully when applying pesticides.
In New Hampshire, consult your county Cooperative Extension Agricultural Field Specialist for the most recent control recommendations for the plants or crops in question.
Post image: Adult Asiatic Garden Beetle. Credits: Mike Reding and Betsy Anderson, USDA Agricultural Research Service, Bugwood.org.