Sap Beetles
Carpophilus spp.
Picnic Beetle Glischrochilus quadrisignatus
Figure 1. Sap (or Picnic)
Beetle Adult
Description
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.
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.
Damage
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.
Figure 3. Sap (or Picnic)
Beetle Larva
Control
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.