Egg - The white, sausage-shaped egg is pointed at one end. It is approximately 1.2 mm long and 0.25 mm wide.
Larva - When mature, the yellowish or pinkish-white grub is about 5.5 mm long. It has a translucent spiny body with 3 pairs of short legs near its head.
Pupa - The lightly colored pupa is approximately the same size and shape as the adult and darkens as it matures.
Host Plants - This beetle infests apple, corn, peach, tomato, pea, and yucca. It is also attracted to various tree stumps, wounds, acorns, Phylloxera galls, and dropped fruit or nuts.
Damage - Prior to 1950, sap beetles were considered "insignificant scavengers" and no threat to sweet corn. Today they are recognized as secondary pests which usually become problems after corn is damaged by other pests, such as the corn earworm.
Sap beetles are attracted to sweet corn as it tassels. They feed on ripening pollen and chew tassels. Later they move to leaf axils where pollen has fallen and collected. Should mature ears on the plant be damaged, dusky sap beetles eventually will oviposit in the kernels. As a result, ears become contaminated with larvae.
Life History - Dusky sap beetles overwinter as adults in soil or debris near the bases of trees or stumps. Resuming activity in April or early May, they are attracted to tree wounds. Approximately 13 days after emerging, first generation females deposit eggs in decomposing plant material. Later generations often oviposit in silk channels or kernels of sweet corn. Larvae feed on whatever is available when they emerge and eventually pupate in the soil. In summer, 28 to 30 days elapse between egg deposition and adult emergence.
Dusky sap beetles usually are scarce in spring and increase in numbers in fall. In sweet corn, however, sap beetle populations continue to decline after tasseling occurs (approx. 15 June in North Carolina). At least three or four generations occur each year. More generations are possible, especially if beetles develop in corn refuse.
An adequate spray program which controls other ear pests should prevent dusky sap beetles from becoming a problem. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.
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