Info sheet about Controlling the Indianmeal Moth

Indianmeal Moth

Plodia interpunctella (Hubner)

Fact and Fiction

  • Indianmeal Moths are Lepidoptera, members of the butterfly and moth family.
  • They do not emerge from the seed; instead the female deposits her eggs on the grain mass to provide ready food for her offspring.
  • They do not originate in the crop fields.
  • The source of infestation does come from adult females present in static bulk bins, production facilities, warehouses, stockrooms, and store shelves.
  • Very few eggs or young larvae can survive the mechanical processing of birdseed in mixers, conveyors, elevators, seed cleaners, and the freefall into bulk bins.
  • Complete eradication of this pest is not possible.
  • Indianmeal Moths can be controlled through a concerted effort by suppliers, manufacturers, distributors, and retailers of wild bird products.
  • Without active participation by all parties, the consumer may be unhappy to discover the presence of the pest in their purchases (it takes one weak link to break the chain).
  • There is no risk to the ultimate consumer: the birds of the backyard, as most consume similar forms of other insects.

The Problem

The Indianmeal 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. Birdfood is particularly susceptible because it is essentially unprocessed mixtures of natural seeds and grains.

Occasionally, the larvae or "white worms with black heads" crawl up walls and suspend from the ceiling attached to a single silken thread. Other times, a few larvae may be found in a food package along with unsightly webbing, cast skins and frass (fecal pellets). Most complaints occur during the months of August and September, but they often appear in other months as well. Because of the biology of the pest, ignoring the problem can result in severe infestations in warehouses, feed and pet stores, seed mills, and homes.

Know the Enemy!

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 colored "at the wing tips" while the inner 2/3 of the wing "at the basal portion" is light gray to ochre-yellow. Also, the head and thorax are reddish-brown and the hind wings gray.

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 molt four to seven times before pupating. Pupae are reddish-brown and about 3/8-inch long. Eggs are grayish 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 of pallets and store shelving. Some crawl up walls to where the wall and ceiling meet 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.

Control Measures

Suppliers: While Aspen Song is a relatively new brand, Cooperative Feed Dealers has been in the birdfood business for decades. We source Aspen Song ingredients from reputable suppliers with whom we have had many years of experience. While distributors, dealers, and consumers can effectively control the problem with inventory turns, our suppliers cannot. Crops are harvested annually. The next opportunity for fresh inventory is the next harvest season. Some suppliers preserve freshness by using cold storage. Our peanut, sunflower kernel and tree nut supplies are often kept in cold storage after harvesting. These most susceptible ingredients are often purchased only after receipt of a sample of the specific lot to be shipped. We have ingredient specifications that address quality in terms of crop year, moisture content, percent admixture, and aflatoxin. Some vendors are able to fumigate bulk rail cars and trailers prior to shipment, and we occasionally utilize this service.

Production Facility: Good housekeeping practices in storage and packaging areas are essential at this point in the chain. Pheromone traps are used in warehouse areas storing bagged ingredients. Our facility has a new, state-of-the-art air screen seed cleaner through which all Aspen Song products pass. Because early larval stages are small enough to feed on dust and chaff, this step helps in the control of IMM in the finished product.

CFD Warehouse: Housekeeping is exemplary in our warehouse facility. Visitors often comment of the high level of cleanliness. Finished goods arriving from production are fumigated with phosphine gas during the months of August and September. This highly effective fumigant kills all stages of all insect species including eggs, and leaves no residue. Moth suppression traps are in place in the birdfood section of the warehouse year round. Inventory is positioned such that a one month supply is in stock at any time. All received pallets are date coded to assure that the first received are the first shipped.

Dealer's Role: Sanitation and inventory turns are the dealer's most effective tools. All Aspen Song products, both large woven bags and clear poly bags are date coded. Be sure to check dates on your inventory and sell on a "first in, first out" basis. Keep birdfood in a cool and dry location. Sweep regularly to remove spillage. In the stockroom, do not stack product directly against a wall. Instead, maintain a sanitation aisle of 30-36 inches. If infested product is discovered, remove it immediately and wash shelving with hot soapy water before restocking. Use of pheromone traps is recommended as a monitoring device both in the stockroom and discretely in the showroom. If flying adults are present, a pyrethrin-based space spray may be used if your state's regulations allow. Consider a monthly pest control service if you are precluded by law from doing such work yourself. CFD offers Roxide's Revenge Pantry Moth Traps. They are labeled for pet food and bird seed. Consider using them in your store, as well as offering them for sale to your customers.

Homeowner Remedies: When a consumer asks for advice on controlling insects in pet foods and bird seed, you can recommend the traps. Another effective way to arrest a minor problem is to freeze the product for 4 to 7 days. An alternative is to freeze the food for a week, remove it from the freezer for a few days, and then refreeze it for another week. Heat is also efficacious. Microwaving a small quantity of product for five minutes will kill insects. Baking in an oven on a shallow pan at 140 degrees for one hour or 120 degrees for two hours will affect a kill. Adults need to have access to the seed in order to lay their eggs in it. Therefore, birdseed should be stored in containers with tight-fitting lids, like metal garbage cans, in garages or outbuildings. Cool and dry, rather than warm and damp, are the preferred storage conditions. If the seed is to be kept in the home, it is even more important that a tight, sealed container by used.

Indianmeal Moths are a persistent issue in the pet food and seed business. Our products are very popular consumer products. It behooves those of us in the distribution chain to do our part to minimize problems with this pest. Cooperative Feed Dealers will continue to do all it can to assure your customers of the best possible products for them to attract songbirds to their feeders. Join us in our collaborative effort to achieve the goal of satisfied customers.

Source of the Images, "The Problem" and "Know the Enemy" Sections: Ohio State University Extension Fact Sheet:
Indianmeal Moth, HYG-2089-97 by William F. Lyon.