By Eric Middleton, UC Cooperative Extension IPM Advisor, for Let’s Talk Plants! October 2023.
Editor’s note: Please welcome Eric Middleton, the new bug man to The Bug Man column of Let’s Talk Plants!
Green Fruit Beetles - A Sign of Summer and Early Fall in San Diego
A loud buzzing… A flash of metallic green… What was that?
A common sight during summers and early fall in San Diego, you’ve probably observed green fruit beetles in your neighborhood. Green fruit beetles (GFB) have many common names: figeater beetles, green fig beetle, western green June beetle, but are known by the scientific name Cotinis mutabilis.
Adult Identification Adult beetles are large, often over an inch long, and are easily recognizable by their distinctive coloration. Seen from above, GFB are a matte metallic green with tan coloration on the outside edge of their wing covers. On the underside, GFB are a bright, shining metallic green. They have short, horn-like projections on the front of their heads, and short clubbed antennae. While flying, adults make a distinctive loud buzzing sound. Although they are noisy and can be startling, GFB do not bite and pose no direct threat to people. GFB are striking insects and are quite beautiful if you get to see them up close.
Lifecycle
While you are most likely to see adult beetles, GFB spends most of their life living in the soil as larvae. In the late summer and fall, mated female beetles lay their eggs just below the surface of organic matter (frequently compost, mulch, or manure). These eggs soon hatch into larvae. Larvae are large off-white grubs, usually found slightly curled in a c-shaped position. You may encounter larvae if digging through the soil or turning over a compost pile. While the adults die off in the fall, the larvae survive over the winter feeding on decaying matter in the soil around them. Larvae grow in size and develop through 3 instars before forming pupae in the spring. Pupae develop inside of hollow cells made of the surrounding soil that resemble small dirt balls. Adults emerge from the ground beginning in early summer. GFB adults are strong flyers and can travel relatively long distances in search of food or a place to lay eggs.
Pest Status and Damage Unfortunately, as their name implies, GFB are strongly attracted to the scent of ripe fruit and adults are an occasional pest of various soft-skinned fruit. Adults can chew into the flesh of figs, apricots, cherries, peaches, plums, grapes, and caneberries. While mating, adults will aggregate together, sometimes resulting in large numbers present in fruit trees. Unlike some other similar-looking June beetle larvae, GFB larvae are not pests and do not harm the roots of plants while in the soil unless all other food sources are depleted. While they infrequently cause serious damage, GFB adults can be an annoyance for home gardeners hoping to enjoy a harvest of fruit in the late summer.
Management Managing GFB is mostly a matter of prevention, and the most effective way to reduce the impact of adult beetles is to focus your efforts on the eggs and larvae. Remove or cover sources of decaying organic matter like compost piles or leftover yard debris and lawn clippings. If removal or covering is not an option, spreading the organic matter thinly or removing it from directly around fruit trees will make it less attractive to female beetles. If you do suspect GFB larvae are present in your compost, frequently turning the compost will bring larvae to the surface and expose them to predation or make them easier to remove by hand. Adult beetles are most common in late summer and early fall, so choosing fruit tree varieties that are ready to harvest earlier in the season can help prevent feeding damage. Cleaning up fallen and decaying fruit will reduce the smell that adults are attracted to and will also help prevent other pests like ants. Finally, if you have large numbers of adults present on your fruit and need to control them immediately, some adults can be captured using homemade traps. Fill the bottom of a container with a few inches of a 1:1 mixture of water and grape or peach juice. Used 1-gallon milk jugs work well for constructing traps. Next, create a funnel using mesh or another material, and place the narrowest end into the mouth of your container. GFB adults are attracted to the fruit juice, will enter through the funnel, and then be unable to exit. If these methods fail, it is not recommended that you resort to insecticides. It is unlikely to be effective, and you risk harming other beneficial insects.
Closing Thoughts As summer draws to a close and fall begins, enjoy your last chances to see GFB this year! If you find yourself having trouble appreciating these beautiful beetles, try thinking of them like hummingbirds, only clumsier. And if you do find them unacceptably damaging your fruit, make sure to manage any nearby organic material to reduce the number of larvae, and try homemade traps for the adults instead of turning to insecticides. Better to practice good prevention strategies for next year and learn to live with these charismatic beetles in the meantime.
For more information on Green Fruit Beetle, visit the UC IPM website at http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/PESTS/grfruitbeetle.html
Dr. Eric Middleton is the UCCE Integrated Pest Management advisor for San Diego, Orange, and Los Angeles Counties. Eric is passionate about sustainable agriculture and investigating practical pest management solutions. His goals are to conduct research that is directly applicable to the needs of growers, to promote practices that have less of an impact on the environment, and to share his findings in a way that is accessible to everyone.