Green fruit beetle—Cotinis mutabilis
The beetle (Scarabaeidae) is an occasional pest of apricots, figs, peaches, and plums. Adults can fly a relatively long distance and are highly attracted to ripe fruit and the odors of fermentation and manure.
The adult is a large, metallic green beetle up to 1-1/3 inches long. Its body is scarab-shaped with prominent legs and antennae that are clubbed (have multiple plates, or lamellae) at the tip. The grublike green fruit beetle larvae are dirty white or brownish and grow up to 2 inches long.
Green fruit beetle is sometimes mistaken for the Japanese beetle, Popillia japonica, which is less than one-half as long. Japanese beetle is a serious pest in the eastern United States, but is not established in California.
Green fruit beetle adults mate and females lay oval, white eggs in the soil just beneath organic matter. Eggs hatch into larvae about 1 week later. During spring, larvae mature and pupate in a cell of soil particles. Adults can be present from late spring through early fall. Green fruit beetle has one generation per year, spent mostly within the larval stage.
Adult beetles chew maturing soft fruit. The grubs (larvae) do not damage fruit. They burrow and feed in piles of compost, manure, and other decomposing organic matter.
To help avoid this beetle's damage, consider planting cultivars that ripen early instead of those that ripen late. Additionally, harvest fruit early and dispose of fallen fruit. Insecticides are of little value against this occasional pest.
To prevent feeding by beetles, manage the grubs. Thinly spread or remove all piles of manure, lawn clippings, and leaves near fruit trees. To exclude beetles, compost within screened bins or turn compost piles frequently to speed decomposition and to expose grubs, which you can crush or leave to be eaten by birds.
Although managing compost and similar organic matter is more effective at reducing green fruit beetle populations, adults may be captured using homemade traps. Attract adults with a 1:1 mixture of grape or peach juice and water. Place several inches of this liquid bait in a 1 gallon container and in the opening insert a funnel of wire mesh with its widest opening facing up. Beetles attracted by the bait will land in the funnel and be guided to walk down into the container. Once inside, adults will be unable to escape.