Stored-product pests are usually brought into the home in an infested package of food. Initially, infestations are easy to overlook because the insects involved are quite small, especially in the egg and larval stages. Often the first indication of the infestation is the appearance of small moths flying about or the presence of beetles in or near the food package.
PANTRY PESTS IDENTIFICATION AND LIFE CYCLES
The most common insects infesting food in the home are in the insect orders Lepidoptera (moths) or Coleoptera (beetles). Adult moths and adult beetles are easy to distinguish from each other, but their larvae are a little more difficult to identify. Use a hand lens to examine the legs of the larvae. Beetle larvae are either grublike and legless or have only three pairs of legs, all located close to the head. Moth larvae have three pairs of true legs, plus additional leglike structures further down the abdomen. Both larvae and adults of beetles feed on foodstuffs, whereas only the larval stage of moths consumes stored products.
Indianmeal Moth. The most common species of meal moths found in the home pantry is the Indianmeal moth, Plodia interpunctella. All damage is done by the larvae, which attack a wide range of products, including cereal and cereal products, flour, cornmeal, rice, dried fruit, dehydrated vegetables, nuts, chocolate, candies, and other confections. When infestations are heavy, mature larvae can often be found in parts of the house far from the original food source because they move quite a distance to pupate.
The Indianmeal moth is a fairly distinct small moth with reddish brown forewings that have a coppery luster on the outer two-thirds and are whitish gray on the inner or body portion. The female moth lays its eggs singly or in groups on food material. Eggs hatch within a few days into small, whitish caterpillars.
Larvae of the Indianmeal moth spin a web as they grow and leave behind silken threads wherever they crawl. When fully grown, the larva is about 1/2-inch long and white with a greenish or pinkish hue. This larva spins a silken cocoon and transforms into a light brown pupa, from which the adult moth later emerges. The Indianmeal moth takes about 6 to 8 weeks to complete egg, larval, and pupal stages during warm weather.
Don’t confuse Indianmeal moths with clothes moths, which are smaller and have more hair than pantry moths. For more information see Pest Notes: Clothes Moths, listed in References.
While there is only one major species of moth that feeds on food products in the home, several species of beetles commonly attack a wide variety of foods: the warehouse beetle (Trogoderma variabile); the sawtoothed grain beetle (Oryzaephilus surinamenis) and the merchant grain beetle (O. mercator); the confused flour beetle (Tribolium confusum) and the red flour beetle (T. castaneum); and the drugstore beetle (Stegobium paniceum) and the cigarette beetle (Lasioderma serricorne). Other beetles that feed primarily on seeds or whole grains include the lesser grain borer (Rhyzopertha dominica), the bean weevil (Acanthoscelides obtectus), the granary weevil (Sitophilus granarius), and the rice weevil (S. oryzae). These seed beetles are not covered in detail here, but their management is similiar to the other pantry beetles.