Lesser Grain Borer
Key Features
This is one of the smallest of the grain-infesting beetles, but one of the most important. The adult lesser grain borer (Rhyzopertha
dominica) is about 3 mm long, polished dark brown or black, and has a somewhat roughened surface. In common with other
bostrichid insects, which are principally woodborers, the lesser grain borer is almost cylindrical, and the head is vertically deflexed
under the thorax so that it cannot be seen from above. Likewise, this insect, though small, has powerful jaws with which it can
bore directly into wood . Wood may once have been its original food. It can eat its way into wooden and paper boxes, and may
destroy book bindings.
Biology
The female lays 300 to 500 eggs, singly or in clusters, in the loose grain. They hatch in a few days. The larvae moult 2 to 4 times.
They may feed on the flour produced by the boring of the adults, or may bore directly into kernels that have been slightly
damaged. They complete their growth within the grain, transform to white pupae, and the adults cut their way out. The life cycle
takes only a month or two, depending on the temperature. The adult lesser grain borers chews grain voraciously causing damage
which may facilitate infestation by a secondary pest. It is a strong flyer and may rapidly migrate from infested grain to begin new
infestations elsewhere.
Distribution
Originally native to the tropics, it has spread through commerce to all parts of the world. It is most prominent in the United States,
southern Canada, Argentina, India, and Australia. In the United States, it is particularly widespread in the Gulf states.
Significance
This is one of the smallest of the grain-infesting beetles, but because infestations can remain undetected for extended periods,
it can be one of the most important.
Control
The first step in managing an infestation is to find and remove the source of the infestation Lesser Grain Borers can feed and
survive on even the smallest bits of grain, so cleaning is a crucial part of controlling these pests. In large-scale infestations,
fumigation (the treatment of the infested material via the application of toxic gas) may be appropriate.
