These are relatively new problems that I never encountered during my past 50 years of berry picking. Only during the last several years have these bugs become a widespread problem, prompting many questions from gardeners, and prompting responses from state universities for how to control them.
There are two insects appearing in homeyard berry patches, especially raspberries.
- Sap beetles, also called picnic beetles, are small black beetles about 1/8 inch long that can be seen on the outside of the fruit, or sometimes on the inner cup of raspberries after picking. They are attracted to ripe fruit of both strawberries and raspberries and can sometimes be found on ripe tomatoes and even sweet corn.
2. Larvae of the Spotted Wing Drosophila (SWD) Fruit Fly are small white maggots that can be seen inside the ripe fruit. The SWD adult is a small vinegar fly, also called fruit flies, and are only about 1/8 inch long, much smaller than houseflies. These flies weren’t observed in the United States until about 2008, arriving from Asia. They lay their eggs in ripening berries, and the eggs hatch into the small, worm-like larvae. The larvae are difficult to see until the berries are picked. If you are unable to see the larvae, but are wondering if they are present, test by placing about 10-20 berries in a water solution of one cup water to which 2 teaspoons salt have been added. Let stand for 15 minutes. If larvae are present, you’ll see them floating on the surface.
How to control these insects: Both sap beetles and SWD are attracted to ripe fruit, so harvesting promptly helps. Practice sanitation by removing all over-ripe fruits instead of leaving them in the patch. Harvest berries just slightly ahead of the “dead-ripe” stage. Insecticide use is tricky, because we are spraying ripening fruit. A product that has proven useful is spinosad. It is a naturally occurring compound that can be sprayed within a day of harvest. Follow label directions. Applications need to be repeated at the recommended intervals of about 7 days throughout the harvest season.
Last season these insects were severe. So far I haven’t noticed them in our own raspberries, but sometimes insect problems become worse in mid-summer.
On a positive note, eating live insects inside berries is considered a delicacy in some cultures. Happy Gardening!