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Visual Reference Library - Insects
 IN-5.0 Larger Grain Borer

Prostephanus truncatus


A beetle 3 to 4.5 mm long and dark brown in colour. It has a cylindrical body shape, when viewed from above the rear of the insect is square shaped. The thorax bears rows of teeth on its upper front edge and the head is turned down underneath the thorax so that it cannot be seen from above.


The larger grain borer usually is restricted to corn (maize) and does not commonly occur north of Mexico. The insect is larger and darker in color than the lesser grain borer.


The larger grain borer is a serious pest of stored maize and will attack maize on the cob, both before and after harvest. Adults bore into the maize husks, cobs or grain, making neat round holes and tunnelling extensively producing large quantities of grain dust as they tunnel. The adults prefer grain on cobs to shelled grain.


Eggs are laid in tunnels and chambers bored by the females in the food source. Larvae hatch from the eggs after three to seven days. The larvae are white, fleshy and sparsely covered with hairs and have three pairs of legs. They develop within the grain or in the flour that accumulates by the feeding action of the adults. They pupate inside the food source.

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Last updated February 2010