Indian meal moth, Plodia interpunctella
The Indian meal moth is the most common species of pestiferous moth in Colorado homes. The larvae feed on and can damage certain foods such as grains, cereals, dried fruits, seeds, nuts, powdered milk, biscuits, chocolate, candy, spices, bird seed, and dry pet food. Adult moths become a nuisance when they fly through homes. These small moths are about 1 cm (3/8 inch) long and have a 1.5 cm (5/8 inch) wingspan. They are generally gray with rusty brown or bronze coloration on the far half of the wing, which is a distinguishing feature of this species. The eggs are small, about 1/2 mm. Caterpillars are cream colored and sometimes have yellowish-green or pinkish shades. The head capsule is dark brown. Fully grown caterpillars are about 1.75 cm (2/3 inch) long and can be seen wandering away from their food source in search of a pupation site.
- The Indian meal moth is a pest of stored grain and can establish in homes if precautions are not taken to reduce the availability of food sources.
- Pheromone traps are an effective monitoring tool for Indian meal moths but alone are unlikely to reduce densities.
- Management involves treating infested materials, cleaning spilled food, and securing potential food sources stored in the home.
Indian meal moth. Note the bronze coloration on the rear half of the wing. Larvae feed on a variety of pantry items such as cereals, dried foods, pet food, and bird seeds. While adults do not feed, they can be a nuisance as they fly through the home. Image credit: Gary Alpert, Harvard University, Bugwood.org
Larva of Indian meal moth. Image credit: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
Pupa of Indian meal moth. Image credit: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
Pheromone trap for detecting Indian meal moths. These traps are effective at capturing male moths and identifying locations where infestations are severe. Alone, they are not likely to be effective at managing infestations. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Life history and habits
All moths have four life stages: egg, larva, pupa, and adult. The larvae develop in many different stored foods such as coarsely ground grains, cereals, dried herbs, dried fruits, and nuts. These moths can also feed on pet foods such as flaked fish food, bird seed, and dried dog or cat food. Ornamental items made of dried flowers or seeds can also serve as breeding sites for these moths.
The moths tend to fly from dusk through the night. Eggs are laid on or near suitable food items. Upon hatching, caterpillars begin seeking out food items for their development. While feeding, they produce silk that loosely binds fragments of food. The caterpillars tend to remain concentrated on the surface of large undisturbed containers. The caterpillars can chew through thin cardboard or plastic bags, and can be found in small, loose food packages.
Caterpillars can reach maturity in as little as one month, depending on food quality and temperature, though the development time is typically much longer. Mature caterpillars migrate away from the food source to pupate, forming cocoons in cracks or confined spaces between walls or in the ceiling.
After emerging from the puparium, adults mate and females can lay over 200 eggs in or near suitable food sources. The adults survive about a week since they do not feed. Several generations are completed annually in Colorado homes, and all life stages may be present since generations overlap. Adults are observed most frequently in the fall and winter.
Traps use sex pheromones that are attractive to male moths. They are useful for identifying locations where infestations are most severe but are not likely to reduce infestations since they do not capture female moths, who will continue reproducing when steps are not taken to remove food sources.
Identifying all sources of an infestation is the most critical step in managing Indian meal moths. The presence of webbing is an effective indicator of infestation. A thorough examination is recommended since Indian meal moth caterpillars can feed on a wide variety of foods. Commonly infested foods include oatmeal, breakfast cereals, nuts, herbs, spices, dried soups, dried fruits, and vegetables. Items that have remained in the pantry for long periods of time should be given extra attention, as well as loosely sealed foods in thin wrapping. Dried dog food, bird seed, dried flowers, and seed-containing craft items should also be inspected. Areas with spilled baking materials such as flour can also harbor Indian meal moths, as can the seed and nut caches of rodents around the home. Any infested material should be disposed of, used, or treated with heat or cold to kill eggs and larvae. For cold treatment, place infested materials in the freezer for two or three days. Heating to 120-140 °F for 20 minutes can kill Indian meal moth but may also damage the infested item. For larger items, longer exposure may be necessary.
Cleaning thoroughly is very important to remove food for surviving insects and prevent reinfestation. Thoroughly vacuuming or sweep areas with spilled food. Susceptible foods should be stored in tightly sealed containers, in the refrigerator, or outdoors until all remaining pupae develop into adults and the remaining moths have died after about a month. All incoming food should be inspected for these pests, and it is recommended that bulk items such as bird seed and dog food be stored away from the pantry area. Pantry items should be placed in tight-fitting containers that are thick enough to prevent entry by the small young stage larvae.
Applying insecticides is not recommended since it is ineffective and potentially harmful if chemicals come in direct contact with food, food preparation surfaces, or utensils. Cracks and crevices near food storage areas can be treated with household insecticides but applications must be restricted to these sites. It is important to note that this will only be effective in conjunction with thorough cleaning and treating of infested items.
Cranshaw, W. 2017. Indian Meal Moth. Colorado State University – Extension. Available https://extension.colostate.edu/topic-areas/insects/indian-meal-moth-5-598/
Utah State University. (n.d.). Indian Meal Moth. Utah State University – Extension. Available https://extension.usu.edu/pests/schoolipm/structural-pest-id-guide/indian-meal-moth