Sap Beetles

Carpophilus spp.
Picnic Beetle Glischrochilus quadrisignatus

The picnic beetle (Fig. 1) is black with four prominent orange or yellow spots on the wing covers, which are shorter than the abdomen. This insect is found in decaying fruit and also in the ears and stalks of corn that has been damaged by the corn earworm and corn borer. The corn sap beetle is a tiny brown beetle found in the ears of corn that have been damaged by earworm or corn borer. The wing covers do not extend over the entire abdomen. The eggs, which are laid singly, are white and slender, resembling a house fly egg. The larvae of both species are active white to cream-colored worms with bromn heads. They pupate in the soil.

Sap (or Picnic) Beetle Adult
Figure 2. Sap (or Picnic)
Beetle Adult

Life History
Little is known about the life cycles of these two beetles. This information comes largely from field observations made by staff members of the Natural History Survey. The insects may winter as larvae or adults in decaying vegetation, debris, and fruit buried in the soil. They emerge in the spring and lay their eggs on spoiling or rotting vegetation. Later they also lay eggs in the silks and kernels of damaged corn. The larvae feed in this decaying material until they are full grown, then they drop to the soil to pupate. Apparently there are two or more generations each year.

These beetles are best recognized by their food habits. Apparently they do not normally attack healthy plants, but work on injured spots on growing plants. They particularly like tomatoes, all fruits, and ears of corn. Growth cracks in tomatoes may be full of these beetles. Over-ripe or bruised apples, peaches, strawberries, and raspberries are also subject to attack. Both species of beetles follow injury to ear corn. Since they lay eggs in the silks, the larvae feed in the ear and are suspected of being primary pests.

Since spoiling plant material is required to attract these beetles, good control of insects and diseases will largely prevent trouble. Pick berries and fruit before they become over-ripe. Handle them carefully to prevent bruising. Destroy all rotting fruits and vegetables. Control of ear-worms and borers means less trouble with corn sap beetles. Thus a clean crop is the best insurance against annoyance by these beetles. Control is rarely justified in commercial field corn. In seed production fields, treatment may be warrented when there are ten or more adults per ear tip on 25% of the plants during the blister or milk stage.