Eight common insect pests - Lesser grain borer

Lesser grain borer

The lesser grain borer is one of the smallest -- and one of the most destructive beetles infesting grain in North America. Lesser grain borers attack most kinds of stored grains but are especially damaging to wheat, rice and corn. Both adult and larval stages cause damage. Until recently, the lesser grain borer was not considered a problem pest in Canada. There are indications, however, that its distribution is expanding, and sightings in Canada have become more frequent over the past decade. The insects have been detected on the Prairies, but they are not likely to survive a prairie winter.

Appearance and behaviour

The adult is:

  • Dark brown to black in color
  • Typically two millimetres long
  • Usually covered with a powdery flour produced as it bores through the kernels

The head of the beetle is hidden beneath the pronotum -- a shield covering the mid section of the insect.

As the name suggests, the insects bore into the kernels to feed, leaving behind a fine powder and particles of feces. They typically consume 17 to 20 percent of each kernel they damage. The rusty grain beetle, by comparison, consumes only four percent of the kernel.


Complete development from egg to adult takes 25 days when the temperature of the grain is 34°C. The female lays about 300 to 400 eggs, and the larvae feed on the kernel remains left by their parents.

Lesser grain borer image

Dorsal view of the Lesser grain borer More on the lesser grain borer
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