Grain weevil (Sitophilus granarius)

Type of pest: Primary pest.

Distribution: It is not exactly known where the weevil originated, though it may have been from the Middle East. The weevil spread across the globe through grain imports and exports. It is found mainly in temperate and other colder climates. It is replaced by Sitophilus oryzae and Sitophilus zeamais in warm climates.

Identification: The weevil is a snout beetle and belongs to the Coleoptera order. Within this order it belongs to the Curculionidae weevil family. Adults are 3-4mm, dark brown, oval, with long legs, and the front of the head has a long snout, elytra are unmarked, wings (elytra below) are missing and the chest has oval punctures. Larvae: apodus. These are small, white, wrinkled, grub-like larvae.

Similar species: Sitophilus oryzae and Sitophilus zeamais.

Life cycle: The life cycle of the weevil is highly dependent on temperature and relative humidity (r.h.). The average lifespan is about one year. The development from egg to adult grain weevil depends on temperature and relative humidity, and is possible between 11 and 30 ºC. The optimum temperature is 30 º C and at an r.h. between 70% and 86%. Under these circumstances, the development takes place in 25 days. On average, it takes about two months to develop.

Larvae are immobile, and develop hidden in the grain. There is generally no external evidence that the larvae have been eating and growing inside the seed until after about one month when the adult weevil chews through the seed coat and emerges. Adults leave a hole in the grain, feed and cannot fly. Immediately after the weevil emerges from the kernel it is mature. However, it takes about 14 days before the female begins to lay eggs. In total, the female lays around 150 to 300 eggs.

Commodities infested: The grains that the grain weevil generally attacks are rye, wheat, barley, corn, oats and rice. To a lesser extent also buckwheat, pasta, macaroni, spaghetti and flour are affected. The damage caused by the weevil consists mainly of quality and weight loss. In addition, the beetles cause nutrition reduction, flavor decay and germination reduction. This is especially true for parties from the developing world. Parties that are particularly vulnerable to damage are those stored for years in moderate to poor storage.

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

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