Stored-Grain Insect Reference/Grain Weevils/Granary Weevil

by the Federal Grain Inspection Service, United States Department of Agriculture

Granary Weevil

The granary weevil, Sitophilus granarius (Linnaeus),^[1] is a small, moderately polished, blackish or chestnut-brown beetle (fig. 1A). The head emends into a long slender snout with a pair of stow mandibles or jaw at the end. This insect is not more than three-sixteenths of an inch long arid often is smaller, There are no wings under the wing covers, and the thorax is well marked with longitudinal punctures, two characteristics that distinguish this insect from the closely related rice weevil with which it is often found.

The granary weevil. one of the oldest known insect pests. has been earned using
^ bike commerce to all parts of the world. It prefers a temperate climate and is more frequently found in the Northern States than in the South.

Both the adults and larvae feed voraciously on a great variety of grains. The adult weevils live, on an average 7 to 13 months. and each female lays 50 to 250 eggs during this period. Before laying, the female uses her mandibles to bore a small hole in a grain kernel. She then deposits an egg through the hole and covers it with a gelatinous fluid that seals the hole. The small, while. fleshy, legless grub or larva hatches from the egg and burrows about inside the kernel. When fully grown. the larva transforms into a pupa and then into an adult.

In warm weather, the granary weevil develops from the egg to the adult stage in about 4 weeks. Cold weather greatly prolongs The developmental period.

Figure 1. Grain weevils: Left, Granary weevil adult; center, Rice weevil adult, right, Maize weevil adult.

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1. Coleoptera, Curculionidae