Indian Meal Moth
The Indian meal moth (Plodia interpunctella)
Kenneth A. Welch
Department of Entomology
The Connecticut Agricultural Experiment Station
123 Huntington Street
P.O. Box 1106
New Haven, CT 06504-1106
Telephone: (203) 974-8483 Fax: (203) 974-8502
The Indian meal moth has four stages in its life cycle.
Adult: The adult Indian meal moth is a small insect with a wingspread of about 3/4 of an inch. The patterned, front wings of the resting adult lie flat along the length of the body. As a consequence, the front one third of the resting adult is whitish-gray. The remaining two-thirds is reddish-brown with a coppery luster.
Egg: The eggs are white, flattened sideways and too small to be easily seen with the naked eye.
Larva: The full-grown, worm-like larva is about 1/2-inch (about 13 mm) long and off-white in color. This color may vary from a greenish to a pinkish hue, depending on the food the larva feeds on. Its head and prothoracic shield are brown.
Cocoon/Pupa: The cocoon is a loose, oval shaped capsule that mature larvae spin around themselves prior to transforming into the pupa stage. The pupa is a capsule-shaped intermediate stage between the larva and the adult. The final formation of adult characters occurs during the pupal stage.
Life Cycle. Adult moths usually emerge, mate, and lay eggs at night. Females lay (oviposit) between 40 to 400 eggs in 18 days, on or adjacent to food material, either singly or in groups depending on several factors. Eggs may also be placed directly on the exterior of packaging material. Eggs start hatching within 4-8 days, usually beginning in April, even with generations overlapping. The 1/16 inch larva soon begins searching for food. Those emerging on the outside of a container are often able to penetrate containers that appear well sealed. As the developing larvae move about, they spin a continuous strand of thin webbing. Over time, this webbing extends throughout the infested material. In a heavy infestation the webbing becomes dense enough to be easily visible.
Larvae mature in 21 to 70 days, depending on food, temperature, and daylength. Mature larvae usually leave their food supply and wander about looking for a place to pupate. Larvae seen on ceilings and counters, etc. are often the first indication of a problem. In heavy infestations, pupation may occur far from the original food source. The life cycle (egg to adult) can take as few as 27 days or as long as 305 days. There are generally four to six generations a year, but the number can vary from one to eight (seven to eight under favorable temperature conditions). During the fall and winter months, larvae will often enter diapause (a form of hibernation) only to emerge as adults in the spring.
Food Infested (Damaged): The larvae of this cosmopolitan insect will feed on cracked grain; coarser grades of flour such as whole-wheat or graham flour and cornmeal (Indian meal) products; dried fruits, shelled nuts and others. Examples include raisins, dried apple, peanuts, chocolate, and powdered milk. Other foods are bird seed, biscuits, bread meal, breakfast foods, cereals, corn meal, corn starch, cookies, crackers, dry dog and cat food, flour, garden seeds, and red peppers. The Indian meal moth has also been reported to breed in shelled or ear corn, matting it over with silken threads. The extensive webbing can spoil more food than the larvae can consume. If any of the foods mentioned above are hidden by mice, or used to make decorations, they are still food for the larval stage of this moth.
The Indian meal moth can be controlled without the use of pesticides. It is important that susceptible food material be stored so that adults and larvae may not have access to it. Glass jars and plastic containers with air tight covers can effectively keep food insect-free. Infestations observed on food stored in either type of storage container are trapped and unable to spread to other food items. Susceptible food items that can not be tightly contained should be consumed within two to three weeks of purchase. When appropriate, the refrigerator and the freezer may also be used for storage of susceptible foods.
The Indian meal moth is the most common insect pest of grain products stored in the home pantry. The four stages in this insect life cycle are the egg, larva, pupa and adult. Larvae seen on ceilings and counters are often the first indication of a problem. The life cycle (egg to adult) can take as few as 27 days or as long as 305 days. The Indian meal moth can be controlled without the use of pesticides. Larvae feed on grain, dried fruit and nut meats. It is important that susceptible food material be stored so that adults and larvae may not have access to them.