Green fruit beetle—Cotinis mutabilis
The green fruit beetle (scarab, family Scarabaeidae), is also called a figeater beetle, green fig beetle, or western green June beetle. The adults are an occasional pest of ripe fruits. Adults can fly a relatively long distance and are highly attracted to ripe fruit and the odors of manure and fermenting fruit.
The adult is a large beetle 3/4 to 1-1/3 inches long. From above it has no apparent hairs and is mostly metallic green with brown or tan along the outside margins of the wing covers. The head has a short, hornlike projection on the face (frons). Its body is oval shaped with prominent legs. The antennae are clubbed with multiple plates (lamellae) at the tip, which is characteristic of adult scarabs.
The grublike larvae are brownish to dirty white. They grow up to 2 inches long and have short brown legs. Larvae feed beneath the surface of organic matter and when exposed they commonly roll onto their back and propel themselves using the stiff dark hairs on their back. Exposed larvae tend to dig their way back down into organic debris and away from sunlight.
Lookalikes. Adults of other beetles that are coppery brown, green, or both are sometimes mistaken for green fruit beetles. Perhaps the most common confusion is with Japanese beetle, which is a serious pest in the Eastern United States but is not established in California. The California Department of Food and Agriculture (CDFA) throughout the state maintains traps for detecting this pest. Where Japanese beetles have been found in California they are targeted for eradication (complete elimination).
Adults of other species that resemble green fruit beetle all lack the horn on the front of the face. Lookalikes include:
- Dogbane beetle (Chrysochus auratus) is a leaf beetle (family Chrysomelidae) about 2/5 inch long. In comparison with scarabs, the dogbane beetle is longer relative to its width and lacks the distinctly swollen plates at the tip of antennae.
- Green June beetle, or eastern green June beetle (Cotinis nitida), is virtually identical to green fruit beetle. An expert dissection and examination of male genitalia may be required to confidently distinguish these species. In California, green June beetle is reported only in the southern part of the state. Adults are 3/5 to 9/10 inch long, on average smaller than green fruit beetle and more variable in color.
- Hairy beetle, or little bear beetle (Paracotalpa granicollis), is about 3/4 inch long. It has mostly brown wing covers and numerous, long, whitish hairs on the sides and top of the abdomen and thorax.
- Japanese beetle (Popillia japonica) has 12 patches of short, white hairs projecting around the abdomen; no other coppery and green beetles have these clumps of hairs. The adult is one-half or less the size of green fruit beetle. Report any suspected findings of Japanese beetle in California to the local office of the county agricultural commissioner or telephone the CDFA Pest Hotline at 800-491-1899.
Green fruit beetle develops through 4 life stages: egg, larva, pupa, and adult. After adults mate, the females lay elliptical to oval, white eggs about 1/10 inch long just beneath the surface of organic matter such compost piles, lawn clippings, organic mulch, and manure. Eggs hatch into larvae in about 1 week. As they feed on the decaying organic matter, the larvae develop through 3 increasingly larger instars. During spring, larvae mature and pupate in a cell of soil particles. Adults can be present from late spring through early fall. Green fruit beetles overwinter as larvae and have 1 generation per year spent mostly in the larval stage.
Adult green fruit beetles chew maturing soft fruit and damage fruit by aggregating on it when mating. The adults are an occasional pest of ripe apricots, caneberries, figs, grapes, peaches, and plums. The grubs (larvae) do not damage fruit or plants; they burrow and feed in piles of decomposing organic matter.
To help avoid this beetle's damage, consider planting cultivars that ripen early instead of those that ripen late. Harvest fruit early and dispose of fallen fruit.
No insecticide application is recommended for green fruit beetle. Manage grubs to prevent feeding damage by adults. Thinly spread or remove all piles of compost, lawn clippings, leaves, and manure that are 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 exposed where they may be eaten by birds or other wildlife.
Although managing organic matter is more effective at reducing green fruit beetle abundance, some of the 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.
Adapted from Pests of the Garden and Small Farm: A Grower's Guide to Using Less Pesticide, University of California Statewide Integrated Pest Management Program (UC IPM).
Adult green fruit beetle.
The adult Japanese beetle has 12 patches of white hairs projecting around the abdomen, which green fruit beetle lacks.
Larvae of green fruit beetle.
Soil pupation cells of green fruit beetle.
Pupa of green fruit beetle exposed in its soil cell.