Extension > Garden > Yard and Garden > Fruit > Integrated pest management for home raspberry growers > Fruit eating insects
Fruit eating insects
Three different beetle species and yellowjackets feed on raspberry fruit during mid-to late summer. Sap beetles (Glischrochilus quadrisignatus and other species), which are also called picnic beetles, are found statewide and will eat both summer-bearing and fall-bearing raspberries. Multi-colored Asian lady beetles (Harmonia axyridis) are found over most of the state and are particularly common near soybean fields and wooded areas. Multi-colored Asian ladybeetles primarily eat fall-bearing raspberries. Corn rootworm beetles (Diabrotica barberi) are only found in the southern third of the state and primarily eat fall-bearing raspberries. All three beetles tend to aggregate on fruit, so that one raspberry fruit may have several different beetles feeding on it at one time. Yellowjackets (Vespula and Paravespula spp.) are common in all parts of Minnesota; they are a problem in raspberries in late summer and fall.
Sap beetles are the most common of all the fruit-eating beetles and the most widespread. These beetles are about 1/4 inch long and dark colored. They often have yellow or orange spots. These beetles primarily eat overripe raspberries.
Multicolored Asian ladybeetle on 'Autumn Bliss' raspberry. Note the M-shaped black marking in the back of the head.
Thaddeus McCamant, Central Lakes College
Multi-colored Asian lady beetles are orange to yellow with black spots, just like native ladybeetles, but are generally larger, about 1/3 of an inch long. The number of spots on the beetles varies from none, to a few, and up to as many as 19 spots. The most reliable identifying characteristic of the multicolored Asian lady beetles is a prominent black "M" shaped marking behind its head. This "M" can look thick, thin or broken in appearance.
Northern corn rootworm beetles are tan to dark green, about 1/4 of an inch long. These beetles tend to be slender and almost rectangular shape. Corn rootworm beetles burrow through the raspberries.
Yellowjackets are about 1/2 inch long, with a slender black and yellow body. They have four wings which they hold over their back when not flying.
Sap beetles usually burrow beneath overripe raspberries. People often don't see the beetles until after the raspberry is picked, and then they find two or three black beetles inside the raspberry cap. Sap beetles primarily feed on overripe fruit that has turned into a dull red or fruit that has been previously damaged.
Multicolored Asian lady beetles feed on the tops of overripe raspberries, often taking a few bites of one raspberry and then moving to other raspberries. Because the skin of the raspberry has been damaged, the raspberries quickly dry out on the cane.
Corn rootworm beetles will burrow into and eat under ripe and fully ripe raspberries. All the fruit that the beetles eat are destroyed. Corn rootworm beetles often attack raspberries and other edible garden plants in large numbers, and can destroy the majority of the fruit during late August.
Yellowjackets are attracted to overripe and damaged raspberries but will also attack ripening fruit as well. If they are present when raspberries are being picked, yellowjackets can sting people.
Sap beetles overwinter as adults and lay their eggs in organic matter. Occasionally, they will also lay eggs in overripe fruit such as strawberries. New adults emerge in July and immediately start feeding on overripe fruit. Sap beetle pressure increases from July through August. There is one generation per year.
Multicolored Asian lady beetles overwinter as adults and lay their eggs on plants in spring. Both the adults and larvae are beneficial, because they eat aphids. In Minnesota, these beetles are especially common in soybeans, helping to control soybean aphids. At the end of the summer, as aphid numbers decline, the lady beetles look for new food sources, and will eat most types of fruit that ripen in late August and September. Like picnic beetles, multicolored Asian lady beetles prefer overripe fruit or fruit that has previously been damaged by birds and other insects. There are two generations per year.
Corn rootworm beetles overwinter as eggs that female beetles lay in late summer and early fall. In the spring, the grubs hatch and start feeding on corn roots. In July, the adult beetles emerge and continue to feed on different parts of the corn plant. In late August, the beetles start moving, and will often find other food sources, including fall-bearing raspberries. By mid-September, the beetles start to die. Raspberries that ripen in the second half of September are more likely to escape damage from corn rootworm beetles than raspberries that ripen at the end of August. There is one generation per year.
Yellowjackets are social insects that construct nests made from papery materials. Their nests are located in a variety of locations, including in the ground, on trees and shrubs, and on or in buildings. Through most of the summer, yellowjackets capture insects to feed to their young. By the end of the summer, when young are no longer are being produced, yellowjackets are more interested in sources of carbohydrates and are attracted to berries and other fruit. Once freezing temperatures arrive in the fall, the workers and the old queen die.
The best management for sap beetles, multicolored Asian ladybeetles, and yellowjackets is to pick raspberries regularly. They are primarily attracted to overripe fruit, and are less likely to be attracted to a raspberry patch that has been picked clean. Insecticide sprays are not recommended for sap beetles, because the beetles are often hidden underneath the raspberry fruit and are protected from sprays. Baited traps can reduce the number of sap beetles in some cases, but will not destroy all the beetles in a raspberry patch. Common traps consist of a container of fermenting plant juices and vinegar. One common trap contains overripe bananas and vinegar. Other people use stale beer or molasses and water with yeast. Place the traps just outside the raspberry patch.
If corn rootworm beetles or multicolored Asian lady beetles are especially common, the plants may have to be protected with an insecticide in order to save the first one or two pickings of the fall raspberry crop. Treating plants to protect against yellowjackets is not effective or practical. When spraying ripe raspberries, be very careful to observe the preharvest interval, i.e. the number of days after the spray before you can harvest. Be sure to check the label of the product you intend to use in order to make sure that it is labeled for raspberries and to verify the preharvest interval. Insecticides that can be effective against beetles include malathion, carbaryl and bifenthrin.
Treat yellowjacket nests when they can be found (see Wasp and Bee Control for specific recommendations). However, yellowjackets can fly several hundred yards when searching for food and their nest may not be on the same property as the garden.