© Stuart M Bennett 2003
Plodia interpunctella
(Indian Meal Moth)

The Indian Meal Moth is considered the most troublesome of the grain-infesting moths. 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,they tend to fly a zigzag pattern around rooms (kitchens and pantries). These moths fly mostly at night and are attracted to lights. Occasionally, the larvae or "white worms with black heads" crawl up walls and suspend from the ceiling attached to a single silken thread. Some adult moths do fly into premises during summer months through open doors or windows, but most "hitchhike" inside in packaged goods and groceries. Not only homes, but restaurants, grocery stores, warehouses, pet stores, seed companies, mills etc., become infested.

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 coloured "at the wing tips" while the inner 2/3 of the wing "at the basal portion" is light grey to ochre-yellow. Also, the head and thorax are reddish-brown and the hind wings grey. 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 moult four to seven times before pupating (see picture below of larvae on prunes). Pupae are reddish-brown and about 3/8-inch long. Eggs are greyish to dirty white and from 0.3 to 0.5mm long.


The female moth lays between 60 and 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 matted with silken webbing. The larval stage is the feeding or "pest stage," and may range from 2 to 41 weeks, depending on the temperature. In stored grains, feeding is done at the surface. When ready to pupate, mature larvae leave their tubes and spin a 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 overwinter 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 temperate zones and three to four weeks in warm climates.


Stored-grains offer compact food sources for a number of insect pests. Good management practices are aimed at excluding these insects while maintaining grain quality. The longer grain is held in storage, the greater the need to maintain good management practices such as sanitation and residual sprays. When proper management is ignored, populations of insects which have been feeding and reproducing in grain residues are free to infest new grain. Once in the new grain, the insects continue to eat and reproduce. Substantial numbers of grain infesting insects can reduce the value of grain, or render it unfit for processing or feeding. Indian meal moths in the grain result in reduced grain weight and dockage because of contamination by fecal material and webbing.

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. Not only is this a partial method of control but also mainly a method of monitoring, thus assessing in which area the infestation is worst, and enabling treatment to carried out with specificity.

Fumigation should be considered only if an emergency exists. Because fumigants are extremely hazardous, they must be handled with care and by qualified personnel.


Back to main Stored Product Insect page