Pest Spotlight: Meal Moths

By: Gerry Wegner Ph.D.

The meal moth is a stored product pest that occurs throughout the United States, but is less frequently encountered than its smaller relative — the Indianmeal moth, Plodia interpunctella. The meal moth has a wingspan of about 1 inch (about 25 millimeters), but with wings folded delta-style at rest, it appears to be about ½ inch (13 millimeters) long.

Unlike the Indianmeal moth, which has distinctly bi-colored forewings, the meal moth has three distinct color zones on each forewing: the innermost and outermost zones are chestnut brown and the median cross-band is light brown or tan (see accompanying photo).

The larvae are creamy white with black head capsules and black collar-like prothoracic tergites. They are often tinged with orange toward each end. The final instar (growth stage) measures ¾ to 1 inch (20 to 25 millimeters) long. Larvae may be found in debris-encrusted silken tubes throughout infested food items.

Meal moth larvae do not have quite the same reputation as Indianmeal moth larvae for wandering considerable distances from their food sources when it’s time to pupate.

Meal moths often enter structures from outdoors during warm months. But, like Indianmeal moths, they can be concealed in infested sacks of feed, grain, seed, pet food and other items, and carried indoors by unsuspecting people.

Pest management professionals (PMPs) may face challenges while attempting to seek out the sources of meal moth infestations in situations where mice and squirrels have stashed away seeds, nutmeats, and pet food in attics and structural voids of buildings. Furthermore, rodenticide baits in garages and basements may be used by meal moths as larval food. Meal moth larvae are known to damage burlap sacks containing foodstuffs when they chew exit holes through the burlap in the process of locating sites to form cocoons and pupate.

BIOLOGY

Meal moths use a wider variety of larval foods than Indianmeal moths, and a damp environment is preferred for larval development.

Mated female meal moths deposit 200 to 400 eggs on or near the larval food. Eggs may be deposited on seeds, cereals, nutmeats, pet foods, dried fruits and vegetables, hay and other dried plant material (in either sound or damp, spoiled condition).

Larvae develop through six instars, feeding from either end of their protective silken tubes formed within foodstuffs. Full-grown larvae exit the food items and, on nearby surfaces, spin whitish silk cocoons with food debris and feces attached.

Development from egg to adult may occur in as little as six to eight weeks in warm weather and heated buildings. When larval development and pupation occur in cooler settings or pupae are subject to autumn and winter cold, however, development may require several months — adult moths may not emerge until the following spring or early summer. Adult females live about one week.

IPM MEASURES

• Remember that meal moths prefer more damp conditions than Indianmeal moths for larval development.
• Inspect for potential larval food items in living and storage areas of buildings, including attics, cellars, crawlspaces and garages. Contain and remove infested items from buildings immediately.
• Look for holes, which are evidence of larval chewing damage to sacks, bags and packages containing foodstuffs.
• Use sticky monitors with pheromone and food lures proven to attract male and/or female meal moths to help locate indoor sources of infestation.
• Use a pest vacuum cleaner with hose attachment to remove moths, larvae, cocoons and spilled food debris from surfaces near larval-infested items.
• Place new and opened packages of vulnerable foodstuffs in resealable, air-tight food-storage containers.
• Ask retailers and warehousers of packaged foods to observe a “first in, first out” policy.
• Keep outside doors and windows tightly closed when not in use.
• Where allowed, apply a light coating of an appropriately labeled, non-repellent residual insecticide to the interior surfaces of rodenticide bait stations when these must be used indoors.

Wegner is the technical director and staff entomologist of Varment Guard Environmental Services in Columbus, Ohio. You can reach him at 614-794-8169 or e-mail gerry.wegner@varmentguard.com.