The Indian Meal Moth is considered the most troublesome of the moths in Canada. Damage is caused by the larvae spinning silken threads as they feed and crawl, thus webbing food particles together. Besides infesting all cereal food products and whole grains, larvae also feed on a wide variety of foods and feeds such as dried fruits, powdered milk, cornmeal, flour, raisins, prunes, nuts, chocolate, candies, health food and seeds, bird seed, dog and cat food, fish food, graham crackers, dried red peppers, pastas, etc.
Sometimes mistaken as clothes moths, homeowners first notice small moths flying in a zigzag fashion around rooms (kitchens and pantries) in the home. These moths fly mostly at night and are attracted to lights and may appear in the living room near or in front of television sets. Occasionally, the larvae or “white worms with black heads” crawl up walls and suspend from the ceiling attached to a single silken thread. Other times, a few larvae may be found in a food package along with unsightly webbing, cast skins and frass (fecal pellets). Packages of whole wheat, graham flour and corn meal are often infested. Most complaints in Canada occur during the months of July and August, but often appear in other months as well. Some adult moths do fly into the home during summer months through open doors or windows, but most “hitchhike” inside packaged goods and groceries. Not only homes, but also restaurants, grocery stores, warehouses, pet stores, seed companies, mill, etc., become infested.
Adult moths are about 3/8-inch (8 to 10mm) long when at rest and have a wingspread of about ½ to ¾ 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.
Life Cycle and Habits
The female moth lays between 60 to 300 eggs, singly or in clusters, on or near the foodstuffs. Eggs hatch in 2 to 14 days with larvae or “tiny whitish caterpillars” dispersing within a few hours. Larvae move to foodstuffs, and feed in or near a tunnel-like case of frass and silk, which they web together. Some food becomes mated with silken webbing. The larval stage is the feeding or “pest stage,” and may range from 2 to 41 weeks, depending on the temperature.
When ready to pupate, mature larvae leave their tubes and spin silken cocoon. They often migrate or “wander” a considerable distance from their food source before finding the pupation site, often in cracks and crevices. Some crawl up walls to where the wall and ceiling meet or crawl to the top of the cupboard to spin the cocoon in which they pupate and from which new adult moths emerge. Mating occurs and the life cycle is repeated.
The life cycle may range from the shortest period of four weeks to the longest of 300 days. Under good conditions, the entire life cycle requires six to eight weeks. However, in cold climates, larvae over winter and pupate in March. Moths emerge in April. Generations overlap as the season progresses. There may be five generations per year in some locations. The life cycle depends on temperature, taking two to six months in temperature zones and three to four weeks in warm climates.
1. Before purchasing, examine foods such as milled cereal products, flour and dried fruit infestations. Examine broken and damaged packages and boxed to avoid bringing stored pests accidentally into the home. Check the packaging date to ensure freshness.
2. 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 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.
3. Foods of questionable infestations or even lightly infested can be super cooled 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.
4. Careful sanitation is the best method to avoid stored product pests. After removing all food, food packages, utensils, dishes, etc. from the cupboard, shelves or storage area, use a strong suction vacuum cleaner with proper attachments to clean up spilled foods (toaster crumbs, cornmeal, bits of pet food, raisins, etc.) from cracks and crevices, behind and under appliances and furniture. Pull out heavy appliances from the wall and scrub with soap and hot water. The ability of these insects to find a small amount of food and survive is amazing. After shelves is thoroughly dry, cover with clean, fresh paper before replacing with food or cooking utensils. Remove and destroy any cocoons found in cupboards and other sites.
5. 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. 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.
6. Pheromone traps are commercially available for inspection, monitoring, and pinpointing infestations of adult Indian Meal Moths. Insects use pheromones to communicate with each other, and are natural compounds created in the insect body. Many have been isolated in the laboratory and now used to lure insects into sticky traps. Adult moths live only five to seven days with their major function to reproduce. Male moths are attracted to pheromone scent (sex-attractant) Traps can be hung indoors next to the ceiling, behind shelves, etc. to capture moths on a sticky board. In food warehouses, some use five traps per 1,000 square feet. A few well-placed traps can detect moths.
7. The use of insecticides is discouraged around food materials. However, aerosol sprays of synergized pyrethrins, labeled for this use, will control nuisance moths flying around rooms. (Follow label directions and safety precautions). If the problem becomes sever and widespread, contact a reputable, licensed pest control operator, who has the training, experience, equipment, and insecticides to get the control job accomplished.