Larger grain borer (Prostephanus truncatus)

Type of pest: Primary pest.

Distribution: Native to the extreme southern USA to northern South America, introduced to Africa in 1980s, becoming widespread.

Identification: Adults are 4 mm, black, cylindrical in cross-section. The head is bent downwards, concealed. The tip of the abdomen is square, while the boundary between the end and side of elytra is marked with a ridge. Larvae: scarabaeiform, with legs fully developed.

Similar species: Dinoderus, Rhyzopertha.

Life cycle: Optimal conditions in 26 days at 30 ºC and 75% r.h. Although the larger grain borer develops best at high temperature and relatively high humidity, it tolerates dry conditions, and may develop in grain at low moisture in contrast to many other storage pests, which are unable to increase in number under low moisture conditions. Eggs are laid on the commodity or in tunnels bored by adults. Larvae are internal feeders producing lots of flour, and are immobile when mature. Adults are long-lived, feed and bore in commodities and can fly.

Commodities infested: It is a pest of stored maize and dried cassava. Both adults and larvae feed internally on maize grains and an infestation can start in the field (when the cob is still on the plant) but most damage occurs in storage. The larger grain borer is a serious pest of stored maize and dried cassava roots, and will attack maize on the cob. Adults bore into the cassava or maize husks, cobs or grain, making neat round holes and tunneling extensively producing large quantities of grain dust as they tunnel. The adults prefer grain on cobs to shelled grain, thus damage to unshelled maize is greater than on loose, shelled maize.

Treatment: Controlled Atmosphere for infestation in product
Treatment: Heat Treatment for infestation in buildings

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