The Indian meal moth is probably the most important and most frequently encountered pest of stored products found in the home and grocery stores in the United States. Of Old World origin, it is now found worldwide. It was given its common name by an early American entomologist (Asa Fitch), who found it feeding on cornmeal (Indian meal).
When at rest, the adult moths are about 3/8 inch long from the tip of their head to the tip of their wings (see the left photograph above.). The front part of the wings are gray, with the outer 2/3’s reddish brown with a coppery luster. The adult moths do not feed on items in the pantry; they simply lay eggs in and on your stored food. Rather, it is the immature larval forms – small worm-like creatures - which do all of the feeding and damage.
The adult female lays 100-400 eggs, singly or in small groups, on or in the larval food material during a period of 1-18 days. Upon hatching, the larva establishes itself in a crevice of the food material. It feeds in or near a tunnel-like case it has webbed together. The larval period consists of several stages and lasts 13-60 days, depending primarily on temperature, moisture and food availability. When the last instar larva is ready to pupate, it leaves the food and wanders about until a suitable pupation site is found. There are usually 4-6 generations per year (range 4-8), with the life cycle (egg to egg) typically requiring 25-135 days.
The larvae are surface feeders and generally produce a lot of webbing throughout the infested part of materials. They are general feeders and attack grain products, particularly the coarser grades of flour such as whole wheat, graham flour and cornmeal, oatmeal, barley wild rice, quinoa, but they can breed in shelled or ear corn. Other at-risk items are a wide variety of dried fruits, seeds, nuts, graham crackers, powdered milk, biscuits, chocolate, candies, dried red peppers, dry dog food, bird seed and flaked fish food. With the last three items, be aware that storage of those items in other locations such as garages, basements and bedrooms may also be at risk. Finally, ornamental items made of dried flowers and seeds may also serve as a food source.
When the larvae wander about looking for pupation sites in homes, they are often mistaken for clothes moth larvae. Likewise, when the moths are flying, they are also mistaken for clothes moths. Adults are attracted to light.
Other Pantry Moths
- Carpet/tapestry moth (Trichophaga tapetzella) with basal 1/3 of front wing dark down to black, remainder of wing white mottled with gray and black.
- Other small moths lack front wing with basal 1/3 pale and remainder dark, wing span of about 5/8-3/4” and /or hind wing broader than front wing and fringed with long hair-like scales.
- Other pantry pests, such as carpet beetles, flour beetles, rice and granary weevils, spider beetles and mealworms will be discussed elsewhere.
The first step is to identify all sources of infestation. The presence of some webbing is usually the most effective way to determine which items are infested
This examination must be thorough, as the range of materials potentially infested is so broad. First go through items discussed earlier. Pay particular attention to items that have remained in the cupboard for long periods. Foods that are loosely sealed, or are in thin wrapping are more likely to be infested than materials in insect resistant containers such as hard plastic or metal.
Indian meal moth may also be found in other materials around the home. Dried dog food and bird seed should be checked. Dried flowers and some craft items that include seeds may be infested. Areas where flour and other materials used in baking may have spilled can support Indian meal moth. Larvae are also known to occur in the stored caches of seeds and nuts that squirrels and other rodents may have in or around the home.
Infested material should be immediately discarded, or somehow treated to disinfest if you wish to save them. Treatments involve using heat or cold to kill any larvae and eggs that may be in the food. Cold treatment requires putting infested items in deep freeze for at least two or three days. Effectiveness of cold treatment may be improved by alternating freezing treatments with rewarming to room temperatures for a day. High temperature treatments involve oven heating at around 120 to 140 degrees F for 20 minutes. (Somewhat longer intervals are needed if treated items are bulky, requiring longer periods to raise internal temperatures.) Injury to the food is possible with excessively high temperature treatments. Also remember that heat or cold treated objects are capable of being immediately re-infested as long as such pests remain in the home.
Since insects also can develop on spilled food, thoroughly clean areas where food was stored by vacuuming or sweeping up all spilled food. The thoroughness of the cleaning is important primarily to eliminate food for surviving insects to feed on. . Although adult moths may only live for a week or so, larvae that have recently pupated in hidden areas of the home may also be a potential source of re-infestation. Therefore all pantry pests must be denied access to all food sources. For the future, place foods in tightly sealed containers.
Although Indian meal moth and other pests can be eliminated, re-infestation is always possible through accidental reintroductions. Consideration should be given to how bulk foods are stored. Bulk seeds and other commonly infested foods (e.g., bird seed, dog food) should be stored in pest-tight containers away from the pantry area. Foods in pantries should be stored in containers that are tight-fitting enough to prevent entry by the minute early stage larvae and must be thick enough to prevent it being penetrated by the larvae.
There are available traps for Indian meal moth that are baited with an attractant known as a sex pheromone. This is the chemical used by the female Indian meal moth to attract males. Such traps are very useful to identify “hot spots” of infestation. However their ability to control Indian meal moth is highly doubtful, despite occasional claims to this effect by suppliers. This is because the traps only capture males, and usually only a fraction of these. As mated females are not captured, they will continue re-infestation. These traps are available for sale through Augustine Services.
Never apply insecticides in a manner that allows direct contact with food, food preparation surfaces or food utensils. Use of insecticides within the pantry area is best done by the highly trained technicians of Augustine Services.