By Whitney Cranshaw, Colorado State University Cooperative Extension, Entomology
The Indian meal moth (Plodia interpunctella) is an extremely common insect found infesting food products in Colorado homes.
Almost any coarse grains (oatmeal, grits, etc), nuts, seeds, dried pet foods, candy bars, spices, cocoa, dried fruits or vegetables (e.g., chilis) are suitable materials for Indian meal moth development. However, flour is rarely infested by Indianmeal moth.
The adult stage of the Indian meal moth is about one-half inch in length, generally gray in color with the bronzy wing tips. The moth is the most common small moth found flying in Colorado homes. Feeding damage is done by the larvae ('worms') which are usually light colored (pale yellow to pink) with a dark head. When feeding the larvae produce webbing that is mixed with food particles and droppings.
Indian meal moth occurs throughout the United States and most household infestations originate from the inadvertent purchase of infested products. During warm months, localized movements of the moths may also occur outdoors, resulting in household infestations in this manner. Because of the broad distribution of the insect, it is rarely possible to definitely establish the original source of a meal moth infestation unless detected at purchase.
Eggs are laid by the adult moths near suitable food, such as along cracks or folds of packages. The newly hatched larvae are very small and are capable of penetrating into loosely closed packaging. Upon reaching a suitable food, they begin to feed. Development can be rapid under favorable conditions and the larvae ultimately reach a length of about one-half inch. Pupation then occurs after which the adult moths emerge. Adult female moths are then capable of laying 200-400 eggs during their lifetime of several weeks. Complete development of the Indian meal moth varies due to temperature and food but typically requires at least a month to complete.
Control of Indian meal Moth
When insects are detected in food products, attention should first be given to identifying all sources of infestation within the home. Check all susceptible food items in cupboards, paying particular attention to items that have not been used for a long period of time. Bird seed, dry dog food, fish food and other such materials are commonly infested items that should not be overlooked.
The physical presence of the insects is the most obvious means of detecting areas of infestation. The presence of webbing is an easy means of detecting items infested by Indian meal moth. Larvae wandering from the infested food items are a symptom that is commonly first detected in the fall of the year. Also, the small brown moths may be seen fluttering about, usually between October and January.
Items infested by Indian meal moth should be immediately discarded or temperature treated in a manner to kill the insect. Cold treatment can involve putting infested items in deep freeze for 3-4 days. Effectiveness of this treatment is improved by alternating freezing treatments with a periodic rewarming to room temperatures is particularly effective for control. High temperature treatments involve oven heating at 133-1400 (F) for 20 minutes. Injury to the food is possible with excessively high temperature treatments.
Heat or cold treated objects are capable of being reinfested so they should be kept in the refrigerator or stored into tight fitting containers until household infestations have been eliminated. Adult Indian meal moths deprived of food might live 3 to 5 weeks. Often bleach or other sanitizing agents are used during this clean up phase. These can kill a few exposed insects and eggs. However, they have not residual effects and provide little additional insect control unless the spilled foods are completely eliminated.
As a routine precaution, materials suspected of harboring developing meal moth larvae should be treated by freezing after purchase. Purchasing smaller amounts of food and rapidly using food products after purchase also prevents infestations from being established from insects brought in on the food.
Photos: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010