During the last week of August, I received a corn sample that had an infestation of whitish colored larvae on the ears. These larvae were feeding on the ears and making holes into intact kernels. Also small in size, dark brown beetles were found in this sample. The insect specimens were identified as the dusty corn sap beetle.
Sap beetles are secondary pests of corn; they are opportunistic invaders that detect damage due to other pests. Adult sap beetles feed on corn silk and pollen and chew on tassels; larvae feed on kernels as described above. There are studies that show high numbers of sap beetles in ears damaged by corn earworm. Corn earworms and other pests (e.g., Japanese beetles) provide entry sites for the sap beetles.
Description of Sap Beetles & Life Cycle
Larvae of corn sap beetle are approximately 1/4 inch long, white with a light brown head, and with hardened projections from the end of their abdomens that are species-specific. Adult sap beetles can be recognized by their dark brown color and short wings that do not cover the entire length of the abdomen; they are near 1/8 inch in length and have antennae with eleven segments. The antennae are slender except for the last few segments, which are distinctly enlarged into a club.
These beetles overwinter as adults in sheltered areas; in spring, eggs are laid on decomposing vegetation or in the ground. Sap beetles can complete their life cycle in 20 to 45 days depending on temperature, and they can have many generations per year.
Management
The use of insecticides for the control of sap beetles on field corn is not practical. In areas where the problem is frequent, plowing under crop debris will reduce overwintering and breeding sites for sap beetles.
Categories: Kentucky, Crops, Corn