Indian Meal Moths

Order: Lepidoptera
Family: Pyralidae
Scientific Name:  Plodia interpunctella

The Indian meal moth is probably the most important and most commonly encountered pest of stored-food products found in U.S. homes and grocery stores.  This lepidopteran is world-wide in distribution.

Biology and Habits

Adult Indian meal moths are crepuscular, that is, most active at dusk.  Once fertilized, female moths deposit 100 to 400 eggs during a 1- to 18-day period.  Upon hatching, the larva establishes itself in a crevice of food material.  It webs together a tunnel-like case made of frass (fecal matter) and silk, and feeds inside or nearby.  The larval stage ranges from 13 to 288 days, depending primarily on temperature and food availability.

Pupation takes place away from the infested material.  When the last instar larva is ready to pupate, it leaves the food source and wanders about until it finds a suitable pupation site.  There are usually 4 to 6 generations per year with an average life cycle (egg to egg) of 25 to 135 days, and can be as long as 305 days.

The adult moths exhibit distinctive scale patterns on their wings.  The upper portion of the forewing is pale gray, whereas the outer portion (away from the center of the body) is reddish brown with a coppery luster.  The underwing is buff in color, and its margins have a feathery appearance.  The wingspan (wing tip to wing tip) is about 5/8 to ¾” (16 to 20 mm) in length.

The mature larva are about ½ inch (9 to 19 mm) in length.  The segmented body is creamy white in color, but also may exhibit a greenish, pinkish, or brownish hue influenced by its food source.  The head and prothoracic shield are yellowish brown to reddish brown in color.  In addition to three pairs of legs, the larva has five pairs of well-developed prolegs that terminate in crochets (hooks).

Control

If possible, perform inspections at dusk when the adults are most active.  Furthermore, inspect light fixtures which attract adults.

A variety of food materials may be infested by Indian meal moths, including chocolates, dried pet food, dried fruits, bird seed, dried flower arrangements, nuts, seeds, powdered milk, graham crackers, wheat flour, and cornmeal.  These destructive pests also damage materials by the presence of their frass and webbing.

Use pheromone traps to locate the source of the infestation.  In addition, by counting the number of adult males captured, the population level may be monitored.

Once infested material is identified, discard the material.  Ensure that all webbing and pupal cases are removed.  After removing all debris, apply an appropriately labeled residual insecticide according to label directions.  A vacuum cleaner or synergized pyrethin aerosol can be used to eliminate adults.  Ultra-low volume treatments or fumigations should be timed with the pest’s flight activity period during dusk for maximum effectiveness.  Efforts aimed at eliminated the adult stage will not solve or control the infestation because the unexposed immature larval stage is the main infestation source.

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(Courtesy of the National Pest Control Association.)