University of Maryland Extension

Pantry Raid - Indian meal moth, Plodia interpunctella

Author: 
Mike Raupp, Professor & University of Maryland Extension Specialist, Ornamental Horticulture, IPM

A number of insects infest stored food products. This includes a variety of beetles and moths that attack spices, grains, dried fruits, cereals, nuts, and pet foods. A cosmopolitan member of the raiders of the closed pantry is the Indian meal moth,Plodia interpunctella. The adult insect is a rather small moth just slightly larger than 1/2 inch in length with wings banded white and rusty red. They flit about the pantry or cupboard in search of mates and tasty products rich in carbohydrates, fats, and proteins.Pies, cookies, cakes, breads, stollens and other delectable holiday treats spring from ovens everywhere during this season of culinary delight. Cupboards and pantries receive lots of attention and activity. In this festive season, many hopeful bakers open pantries only to be greeted by swarms of small flying insects, a most unwelcome surprise. What are these invaders?

One interesting infestation I recently witnessed raged in a package of organic sunflower seeds. Although the package was unopened, the clever female moth laid her eggs on the surface of the crinkly plastic bag. Upon hatching, the tiny larvae, caterpillars in fact, found a small gap in a seam of the package and crawled inside to dine on nutritious seeds. The small caterpillars spun silken galleries from which they sallied forth to eat. As they grew, more silk was produced and the digested remains of the meals, called frass, was voided and entangled in the silken strands to form a nasty messy web. Two excellent clues signaling the presence of meal moths are the presence of silk and frass within a bag of flour, grain, seeds, or pet food. After the larvae completed their development, they gnawed holes in the bag and went nomadic, wandering about the walls and ceiling of the pantry in search of a protected spot to spin cocoons and develop into pupae. Sometimes vagabond larvae enter cracks between shelves, lids of jars, electrical sockets, or seams behind baseboards to pupate. From the pupae emerged the next generation of adults intent on finding new bags and boxes of stored products to infest.

Meal moth caterpillars excavate seeds and generate scores of pellets of frass, a polite term for insect excrement. Frass is often a good sign of a meal moth infestation.

How did these pests arrive in the first place? It is possible that the original infestation of meal moths arrived with cereal, seeds, dried fruit, or grain as a few tiny eggs within a package from the store. After hatching from the eggs, a few small caterpillars in a bag of seeds in the back of a closet are likely to go unnoticed, but these colonists are capable of generating sufficient moths to generate a full blown infestation. Meal moths are also able to survive outdoors and are commonly found in caches of nuts or seeds stored by squirrels or rodents. Adult moths may originate outdoors and invade indoor pantries during warm weather when doors and windows are open. Mice often enter homes in autumn and winter seeking shelter and bringing stockpiles of seeds with them. These seeds and the associated moths may be a source of infestations indoors.

What should you do if you find these rascals in a pantry or cupboard? First, remove all goods and products from the storage area. Vacuum the cupboard, pantry, or cabinet like there is no tomorrow. Carefully inspect all cracks, corners, crevices, and seams in the cupboard and remove any larvae or pupae your find. Seal as many of these refuges as possible with caulk. Remove and replace loose paper used to line shelves. Inspect any pots, pans, glasses or other items occupying the pantry where food will be stored and remove any meal moths on these items as well. Inspect opened and unopened bags and boxes of food for signs of silk, frass, larvae, or moths. If in doubt, toss it out. My pantry pest guru recommends the “deep chill” treatment for unopened packages you might want to salvage, but are suspect by association. Place unopened bags in the freezer for one week, remove them for one week, and then freeze again for a final week. The intermittent week of thaw tricks eggs into hatching and the tiny caterpillars are then killed by the second trip to subzero land.

Strands of silk on the inside of food containers are another clue of a meal moth infestation.

When you purchase items that might serve as food for meal moths, seal them in strong plastic storage containers with tightly fitting lids. This will help prevent any moths you might have missed from laying eggs that hatch into larvae capable of infesting your food. Try not to store prime foods like grain or dried fruit for very long periods of time. The longer stored products remain on a shelf, the more likely they are to be infested by an itinerant moth that happens by. One approach useful in alerting you to an incipient invasion of meal moths is to purchase and deploy pheromone traps. These small triangular boxes are placed inside your pantry or cupboard. Inside is a sex pheromone that attracts the male meal moth from many feet away. The ever-hopeful male senses the pheromone; a chemical signal released by a female, and is tricked into believing that a receptive beauty waits inside the open-ended trap. He flies inside to find his mate, but instead becomes snared by a sticky substance lining the inside of the trap. By placing these traps within a pantry, you can detect the emergence of male moths that may be the harbingers of a burgeoning population of moths in your cupboard. This advanced warning serves as a signal to initiate a search and destroy mission. Adventures like this are always a good way to get some much needed exercise after the holidays and have a clean pantry to boot.

The Handbook of Pest Control, Ninth Edition, by Arnold Mallis was used as a resource.

This article originally appeared in the January 2010 edition of Bug of the Weekand the Winter 2011 edition of Home and Garden News.

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