Granary Weevil Biology

Granary Weevil

Granary weevils are insects that have been a major worldwide pest for centuries. They will infest homes in the cooler climates and in the United States, they may be evident in homes above the middle regions.

Biology and Description

Granary weevils go through a complete metamorphosis which means they will enter all stages of the insect life cycle including egg, larva, pupa, and adult. In a kernel of grain, the granary weevil will lay an egg in the hole that it bore and then seal the hole. If all conditions are favorable, a female granary weevil can lay more than 200 eggs in her lifetime. Only after a few days, the egg will hatch and the larva will begin to feed on the internal portion of the grain until they emerge from the grain itself. Granary weevils go through 4 larval instars before they go into the pupa stage. This takes about a month ranging from 20-35 days. Pupation happens inside the kernel of grain and takes about 5-16 days. They will emerge as an adult and adults will live for about 7-8 months. For an entire life cycle to rotate, it takes only a few months and can be as short as just one month. There are several generations of granary weevils that will overlap in one year. Adult granary weevils can be distinguished by their reddish-brown or almost black color. They are about 3-5 mm long. They can also be distinguished by their pits or indentations in their thorax and elytra (hardened outer shell that covers their wings). Wings are present and greatly reduced so they are not able to fly. Like many other species of weevils, the granary weevil will have an oval shape and their heads will elongate into a snout or beak. The snouts of male granary weevils are wider and much shorter than that of females.

Food and Damage

Granary weevils are attracted to and will attack all kinds of grains and grain products. These products will include such materials as wheat, corn, barley, or rice. In stored food products, they may be found in materials like macaroni or spaghetti. Adults will feed on the same foods as the larvae however, because they do not need to develop in the inside of whole grains like larvae do, they are not limited to just one grain or in other words, they are not restricted in their diets. Because granary weevils are not able to fly, they are usually confined to stored grains and will be primarily transported by man. The granary weevil will be more common in the northern states however, they are found all over the world. Granary weevils do not attack people nor do they attack animals. They also do not damage household furniture.


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Date: Tuesday, 6. December 2011 10:10
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