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Grain Moth

General Facts

Angoumois grain moths will feed, mainly on whole grains and they are named for a region in France in which they were first scientifically described. Often infesting the grain before it is harvested, the larvae of these moths will develop within the whole kernels of corn, barley, rye, oats, rice, and other seeds. Occasionally they will infest caked grain materials. In the U.S. it is considered second only to granary and rice weevils as a pest of stored grain and it is active at low temperatures, so it can cause considerable damage in the winter months to stored grain products.

This moth is also a common household pest which infests decorative Indian corn, popcorn, corn used to fill bean bags, and other whole seeds. However, It prefers damp grain as opposed to old dry grain. These moths will leave a lot of debris on top of infested grain and destroy the uneaten grain by making it foul and unpalatable.

Female moths deposit eggs on grain kernels throughout the crib. Under normal conditions, a female will lay forty eggs. The eggs are glued to the kernel. Larvae emerging from the eggs eat through the kernel and begin feeding on the endosperm or germ. To assist in penetrating the kernel, larvae sometimes spin a cocoon that they use for leverage. Once inside the kernel, larvae continue to feed until mature, enlarging a cavity within the kernel. When mature, the larvae eat a channel to the outside of the seed, and make a weakly fastened flap at the exit by cutting the shell one-half to three-quarters the circumference of a circle. Larvae then spin silken cocoons and pupate within the kernels. Adults emerge by pushing the flap back on the kernels. The life cycle is complete in about five weeks at optimal temperatures.

The adult is a small buff to yellowish-brown moth about one-third inch long with a wing span of one-half inch. The front wing is a lighter color than the hind wing. Both wings end in a thumb-like projection and have fringed rear margins. The eggs are white when first deposited, but soon turn red. Full grown larvae are one-fifth inch long and white with a yellow head. The area near the head is slightly larger in diameter than the posterior portion of the insect.

 

Damage

Angoumois grain moth larvae feed on a number of whole kernel grains. Their feeding causes a reduction in grain weight and quality. Heavily infested grain smells bad and is less attractive for consumption. Corn cribs infested with this insect will contain ears with small holes on individual kernels. Ears throughout the crib will be infested. In bins, however, only the top few inches of grain will be infested.

 

Control

Once the problem is observed, control in crib stored corn can be difficult. Because the crib is open, fumigation cannot be effective without covering the crib with a tarp or plastic to seal in the fumigant. A better alternative is to empty the bin as soon as possible.

As with bin stored grain, sanitation and crib preparation before introduction of new grain can reduce the potential of angoumois grain moth infestations. Thoroughly clean the crib of old grain and ears. Larvae of the insect can be harbored in these residues. Harvest equipment should also be cleaned before use. Unless the ear corn is going to be stored for longer than a year, a residual insecticide is probably not necessary. Although this insect can be a serious problem, few corn cribs have populations high enough to cause concern.