Grain borers (extended information)

Rhyzopertha dominica, lesser grain borer
Prostephanus truncatus, larger grain borer

Description and life cycle

The small, nearly cylindrical beetles are reddish brown to dark brown; their head is turned down and appears to be covered by a hood (Prostephanus truncatus). The larger grain borer is 3mm to 5mm long and cylindrical in shape. The lesser grain borer is 2mm to 3mm long and slim. Both are capable of flying. The beetles lay their eggs on the grain or in the floury dust. The tiny, whitish grubs, feed on the dust or crawl into and feed on slightly damaged kernels. Pupation takes place inside the kernels, and emerging adults then cut their way out of the kernels.

Mechanism of damage

These insects infest both stored grain and maturing maize ears in the field. In a very short time, the adults produce large quantities of floury dust as they bore into and feed on the grains. Damaged grains can readily be identified since they are usually covered by a film of this dust.