Larger Grain Borer (Prostephanus truncatus)

Adult’s tunnel through stored maize grain or other starchy products, such as dried cassava chips, creating large quantities of dust. Larvae and pupae may be found in the tunnels made by the adults. It is extremely damaging to maize when dried and stored on the cob. The adults chew small holes in the kernel and then lay several eggs in the grain or in the grain mass. Damage is seldom noticed until exit holes appear and adults are seen roaming the grain mass.

Identification:
Adult beetle: 3 - 5 mm in length, dark brown to black in colour. When viewed from above the rear of the insect is square shaped. It is similar in appearance to the lesser grain borer with the main differences being its larger size and darker colour.

Larvae: 3-4 mm in length, white to yellowish in colour.

Biology:
Female beetles will deposit 200 – 500 eggs in grains over a 4 -6 month life span. The hatching larvae are immobile and live within the grain or in the flour that accumulates with infestation. Development time from egg to adult depends on temperature & conditions.

Control:
The source of the infestation should be traced. Any affected foods should be discarded. The area should then be thoroughly cleaned, and a residual insecticide labelled for ‘crawling insects’ can be used. Stock rotation should be reviewed to ensure that products likely to be infested are used quickly. In the home, foodstuffs should be stored in tins or plastic containers.

Products to control Larger Grain Borer: