Indoor Entomology

In spite of temperatures in the 50s (10 degrees C) here in Indiana, most of the overwintering insects are still in diapause. Entomologists must turn their gaze indoors. A common winter indoor insect is the Indian Meal Moth. These moths lay eggs in raw or processed stored grains. The caterpillars are adapted to living in dry conditions. The process of making energy combines oxygen with food and releases carbon dioxide and water. The meal moths are adapted to recover a high proportion of the “metabolic water”. This allows them to survive in dry grains. Indian meal moth will grow in “white” flour. However, mixes such as pancake mix or biscuit mix are more nutritious because they contain vitamins and other additives that facilitate growth. Meal moths grow and reproduce more rapidly in these mixes.

The Indian meal moth larvae can chew holes in most containers and plastic bags. This allows them to leave a crowded bag and move to an uninfested one. The meal moth larvae have silk glands that release a silk webbing. A tell tale sign of meal moth is webbing in the opening of a bag or in the flour. Meal moths are easily controlled by placing the infested material in a freezer and discarding it. It is useful to thoroughly clean an infested cupboard and use the opportunity to get rid of those old, out of date products.

Indian Meal Moths are brought into homes in contaminated grains. Grocery stores and food warehouses dislike the meal moths and can take steps to locate pest populations and eliminate them. Indian Meal Moths communicate with pheromones, odors produced by the female moth to attract mates. In the early 1980s, when Indian meal moth pheromone first became available, I was involved in a couple of projects to find ways to use the pheromone.

In one instance, we had a grain exporter who had very low tolerance for meal moths. The plant was fumigated on a routine basis with less than 100 percent effectiveness. We supplied the plant sanitation manager with pheromone traps to place among the pallets ready for shipment. The manager found that two traps had the highest captures and initiated a thorough inspection of the area between the traps. He found a pallet that had been out of the warehouse then returned. Close inspection found a meal moth population in that shipment. Without the pheromone traps, detecting the infested shipment would have been less likely. The trap counts in that section of the warehouse dropped to zero after getting rid of the contaminated pallet.

In a location where grain came into the plant on conveyers, a trap near an old boarded up conveyer had the highest trap catches. This inspired the plant manager to have a crew remove the conveyer. Behind the boards were old bags that had fallen off the conveyer and were now full of meal moths. Eliminating these breeding sites greatly reduced the populations.

Indian Meal Moth, a Common Pest of Stored Foods (About half the size of a penny)

In another study, we surveyed warehouses using pheromone traps. The two most commonly infested commodities were bird seed and pet food. For homeowners, meal moths are a relatively minor problem that can be eliminated by discarding infested foods. We found that the warehouses with the highest meal moth captures all purchased their bird seed from the same supplier. The bird seed contained large populations of meal moths. The tasty caterpillars were a treat for the birds, but a source of infestation for the food warehouse.

Consumers need to be aware of buying foods from establishments that have lax sanitation. If you see tiny copper and gold moths flying around a store, you could easily bring them into your kitchen. If you see tiny copper and gold moths flying around your kitchen, perhaps it is time to check the shelves and clean the cupboards.

About jjneal

Jonathan Neal is a retired Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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