Moths attack stored grain products or household foodstuffs. Once established in food, insect populations can increase and infest vulnerable material throughout the home, apartment, or storage area. Some adult moths do fly into the home through open doors or windows, but most are carried inside from outdoor storage or in packaged goods or groceries.
Everyone’s home is vulnerable. However, those who do not store food properly have the greatest problems. Spilled or exposed foods attract the insects and increase the chance of infestation. Foods that are not tightly sealed, especially those maintained for long periods of time, are particularly susceptible to infestation.
The Indianmeal moth and the Mediterranean flour moth are the most prevalent meal moths which infest foodstuffs in Washington. Several other moths that are found occasionally in foodstuffs include the meal moth, the whiteshouldered house moth, and the brown house moth.
The adult Indianmeal moth, Plodia interpunctella, has a wingspan of about 1/2 to 3/4 -inch. The tips or outer half of the wings are reddish brown or “coppery,” while the basal portions are grayish-white. The larvae are usually off-white but can be pink, yellow, greenish, or brownish. At maturity the larvae are about 1/2 -inch long.
The adult female can lay several dozen to several hundred eggs. The larval stage may last from a few weeks to 9 or 10 months, depending on temperature. The larvae, which spin a great deal of webbing while they are feeding and maturing, are usually found in or near silk tubes. When ready to pupate, larvae leave their tubes to spin a cocoon. They often migrate a considerable distance from their food source while searching for a pupation site, and are found on walls, countertops, and ceilings. This is especially true when infestations are heavy. There can be four to nine generations per year, depending on the food supply and house temperature.
The larval stage is the feeding or “pest” stage. Indianmeal moth larvae appear in grain, cereal and grain products, dried fruit, dog food, candy, dried milk, and many other foodstuffs.
Mediterranean Flour Moth
The Mediterranean flour moth, Anagasta kuehniella, has a wingspan of about one inch. Forewings are grayish with dark zigzag lines; the hindwings are off-white. This moth is most easily recognized by its characteristic resting pose. The moth raises the front of the body, giving the wings a distinct downward slope. The tip of the abdomen protrudes up between the wings. Larvae are white to whitish-pink and about 1/2b -inch long at maturity.
The adult female can lay several hundred eggs. The larval stage normally lasts about 40 days, but can last considerably longer at cooler than optimal temperatures. Under favorable conditions, four to five generations hatch annually. Larvae spin a great deal of webbing on or near their food, as does the Indianmeal moth. These larvae, too, live in silk tubes. Mediterranean flour moth larvae pupate in silken cocoons in clean flour or other food, away from infested material. Mediterranean flour moth larvae generally feed on the same materials as the Indianmeal moth
The adult female meal moth lays about 200—400 eggs. The larval stage sometimes takes as little as 6 weeks. Larvae spin tough silk tubes that are coated or mixed with food particles; they stay in these tubes and feed from the open ends. When fully developed, the larvae leave these tubes and spin silken cocoons in which they pupate.
The larvae of this moth species feed on a variety of grain products. They are generally a problem on food products that are in poor condition, moist, or stored in damp places.
Whiteshouldered House Moth
The whiteshouldered house moth, Endrosis sarcitrella, is not common in household products but is found occasionally, and thus deserves mention. The adults are quite distinctive, having grayish-white wings with dark spots and a “shoulder” area that is bright white. This white shoulder becomes dingy as the adults age. Adults are roughly the same size as meal moths. Larvae are white with brown heads and are about 1/3 -inch inch long at maturity. Larvae feed on grain products, wool or other protein-based carpets, corks, dry seeds, fungi on trees, on rubbish in bird nests, and on other foodstuffs or organic debris which has accumulated undisturbed.
Brown House Moth
The brown house moth, Hofmannophila pseudospretella, is about as common as the whiteshouldered moth. The bronze-brown adult has dark spots on the forewings and is slightly larger than the whiteshouldered moth. Larvae, white with tan heads, are about 1/4 -inch long at maturity. Larvae feed in grain products, furs, paper, carpets, insect collections, dried fruits, and on a variety of other stored products.