Sap beetles in strawberries

Strawberry growers are sometimes perplexed by the presence of round, small, deep holes in the side of strawberry fruit. Occasionally, small dark beetles can be found inside the hole. This damage is typical of injury caused by sap beetles. Sap beetles are a common problem in New York, Ohio and Michigan, but not often in Ontario. In 2012 however, this pest caused some significant damage.

Identification

Several species of sap beetles can cause damage to strawberries. These include the common picnic beetle (beer bug), the Strawberry Sap Beetle and the Dusky Sap Beetle. When identifying these beetles an important feature is the presence of knobbed antenna which is common among all sap beetles. The Strawberry Sap Beetle adult is the smallest of the three at about 3 mm long, and is irregularly marked with shades of brown. Slightly larger is the Dusky Sap Beetle at just over 3 mm in length and dull black. The Picnic Beetle is around 6 mm in length with 4 orange spots on its back. Larvae of all three are off- white with three pairs of legs near a brown head.

Habitat and life cycle

Sap Beetles overwinter in woodlands and also around raspberry canes and blueberry bushes. However, they do not appear to overwinter in strawberry fields. Beetles emerge from overwintering sites when strawberries become ripe in the spring and are most active when temperatures are over 16°C.

Feeding occurs mainly on over ripe and damaged berries but Strawberry Sap Beetle damage is also commonly seen on ripe otherwise marketable berries. Eggs are laid in the soil near damaged fruit, but occasionally in partially consumed fruit. This allows the larvae to feed for about one week, after which they return to the soil to pupate and mature into an adult sap beetle. Three weeks after eggs are deposited the beetles are mature.

Damage

Strawberry Sap Beetle adults damage fruit by feeding their way into ripe strawberries leaving a small round hole that may extend deep into the berry. This type of injury may be confused with slug injury if the slime trail left by slugs is not clearly visible. Picnic and Dusky Sap Beetles commonly feed on damaged fruit, although the Dusky Sap Beetle will lay eggs directly into undamaged sweet corn when populations are high. Although Strawberry Sap Beetles are primarily of concern to strawberry growers, this beetle is known to feed and reproduce in cherries, blueberries and raspberries as well.

Management

Sap beetles are difficult to control using insecticides and treatment may be impractical as the beetles feed on berries that are ready for harvest. Some broad-spectrum insecticides used for tarnished plant bug may provide temporary suppression of sap beetles. However, multiple applications of these insecticides could result in reduced populations of beneficials such as wasps that parasitize the strawberry sap beetle, and beneficial mites that feed on spider mites. Sap beetles are best controlled by picking all ripe and overripe fruit on a regular basis. Destroy or bury discarded berries and other waste fruit and vegetable materials to reduce feeding opportunities for sap beetles.