Indian Meal Moths

Indian Meal Moths Plodia interpunctella (Hubner) is one of the most commonly reported pests of stored grains in the United States. Larvae of the Indian meal moth feed upon grains, grain products, dried fruits, nuts, cereals, and a variety of processed food products. The Indian meal moth is also a common pantry pest.

Adult moths are about 3/8-inch (8 to 10mm) long when at rest and have a wing spread of about 1/2 to 3/4 inch (18 to 20mm). When viewed from above with the wings folded over the back, the outer 2/3 of the wing appears reddish-brown or bronze colored “at the wing tips” while the inner 2/3 of the wing “at the basal portion” is light gray to ochre-yellow. Also, the head and thorax are reddish-brown and the hind wings gray.

The larvae or “caterpillars” are about 2/3 inch (12.5mm) when mature. Brown-headed larvae are dirty white, sometimes tinged pink or green. Larvae are quite active and molt four to seven times before pupating. Pupae are reddish-brown and about 3/8-inch long. Eggs are grayish to dirty white and from 0.3 to 0.5mm long.

Indian meal moths flying in your kitchen throughout warm weather,beginning in April. Adult moths do not feed; theironly purpose is to mate and lay eggs for the next generation. The larva or caterpillar does damage as it feeds on the surface of food, spinning silk as it goes and leaving a mat of webbing and excrement on the food’s surface.

Life Cycle: As long as the temperature within a grain bin or building where grain is stored remains above 50° F, the Indian meal moth can survive and reproduce. A typical life cycle (egg to adult) is completed in forth to fifty-five days. A potential for seven to nine generations per year exists; however, because of cool temperatures during the winter months fewer generations are usually completed. Under optimal conditions, the entire life cycle can be completed in approximately twenty-eight days.

A mature female lays 100 to 300 eggs on food material, either singularly or in groups of twelve to thirty. Larvae begin to hatch in two to fourteen days, depending on environmental conditions. Newly hatched larvae feed on fine materials within the grain and are small enough to pass through a sixty mesh screen. For this reason, it is difficult to exclude larvae from most packaged foods and grain.

The larval stage lasts from two weeks to one year, and is responsible for grain losses. In grain, larval feeding is usually restricted to the top one to two inches. Large larvae feed on the grain germ. When mature, larvae spin a silken cocoon and transform into light-brown pupae. The cocoons and pupae can be seen on the grain surface and walls of grain bins. Adults emerge in four to thirty days, mate, and females lay the next generation of eggs. Adults live from five to twenty-five days.

Damage: Adults do not feed, but they lay eggs on food materials. The larval stage causes the injury. Larvae are generally surface feeders but can feed within the grain. As they feed, larvae spin silken thread webbing throughout the infested food source. Small particles are often adhered loosely to the threads.

Larvae feed on a variety of foodstuffs. They are often found in stored grain, cereals, dried fruits, nuts, seeds, and meal products. They will feed on flour, cake mixes, powdered milk, and chocolate. Two sources often overlooked are birdseed and dry pet food. Frequently, infestations start with moths brought in on these products.

Control: Before purchasing, examine foods such as milled cereal products, flour and dried fruit for infestations. Examine broken and damaged packages and boxes to avoid bringing stored pests accidentally into the home. Check the packaging date to ensure freshness.

Purchase seldom-used foods in small quantities to prevent long storage periods of a month or more. Susceptible material stored for six months or more, especially during the hot summer months, has the possibility of developing into serious infestations. Store susceptible foods in insect-proof containers of glass, metal or plastic ware with tight-fitting lids, ideally screw-type. Highly susceptible foods, such as spices, can be kept in the refrigerator and other foods in the freezer. Always use older packages first, and inspect frequently to avoid any spillage which might attract insects. Properly ventilate the storage area to discourage moisture-loving pests.

Foods of questionable infestations or even lightly infested can be supercooled or superheated. Place exposed or suspect foods in a freezer at 0°F. for four to seven days or in a microwave oven for five minutes or in a shallow pan or tray in the oven at 140°F for one hour or 120°F for two hours. Spread the material thinly to permit effective cold or heat penetration to kill all life stages of the pest. If in the oven, stir food periodically to prevent possible scorching. Dried fruits can be placed in cheese cloth bags and dipped into boiling water for six to ten seconds to kill external pests. However, seeds saved for planting may have the germination reduced after superheating or cooling. Sifting the food material will remove possible insect fragments and any remaining will not cause harm if consumed. After insects are killed, contaminated food might be used outdoors during winter months for bird feed.

Locate the source of infestation and quickly get rid of it. Dispose of heavily infested foods in wrapped, strong, plastic bags or in sealed containers for garbage disposal service or bury deep in the soil if permitted and practical. If detection is made early, it may be the only material infested and the problem is solved. Be sure to carefully examine seldom-used foods, especially in least disturbed storage areas. One can spread suspected foods on a tray to determine whether infestation is widespread. Inspect unopened cardboard boxes since pests can chew into these boxes and plastic inserts.

Consulting a Pest Control professional should be considered if widespread Indian Meal Moths infestations develop.

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