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 damage food by contaminating it with their bodies and their by-products. The larval stage of the Indianmeal moth produces frass (excrement) and webbing, and some beetle larvae produce secretions that give food a disagreeable odor and taste. Setae (hairs) from the warehouse beetle can irritate the mouth, throat, and stomach of people who eat infested products. In addition, pantry pests might introduce microbes into the food that could produce mycotoxins (highly carcinogenic compounds), especially if the food is stored in warm, humid conditions.

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.

                        IDENTIFICATION AND LIFE CYCLES

INDIAN MEAL MOTH (Plodia interpunctella)

Biology

• Length: 5/8 to 3/4 inch

• Wings are pale gray colored at the base while the outer portion is reddish brown.

• Larvae are normally a dirty white color about ½ inch long.

Distribution/Habits

• Found throughout the world

• Infest grain products and a wide variety of seeds and nuts, chocolate, dry pet foods, dry fruits, powered milk, graham crackers, biscuits, dried red peppers, etc.

• Larvae produce webbing throughout infested material.

TROGODERMA BEETLES (Trogoderma)

Biology

• Length: 1/8 to 1/4 inch

• Oval in shape and dark in color

• Wing covers have varying patterns of brownish and yellowish scales.

• Larvae are up to 1/4 inch long.

• Larvae are a yellowish-tan color with a tail of long hairs extending from the tip of the abdomen.

• Species include the larger cabinet beetle, Khapra beetle and Warehouse beetle.

Distribution/Habits

• Pest of fabrics and stored products

• Larvae are present for most of the year.

• Accumulate anywhere where dead insects accumulate: light fixtures, window sills, wall voids or insect light traps.

Sawtoothed Grain Beetle and Merchant Grain Beetle.

The sawtoothed grain beetle and the merchant grain beetle are slender, flat, brown beetles that are about 1/10-inch long. Both beetles have six saw like tooth projections on each side of the thorax (section between head and abdomen). The sawtoothed grain beetle has smaller eyes than the merchant grain beetle and a larger area just behind the eyes. In both larval and adult stages, these beetles feed on all food of plant origin, especially grain and grain products like flours, meals, breakfast foods, stock and poultry feeds, coconut, nutmeats, candies, and dried fruit; it is not uncommon to find these beetles infesting pet food, bird seed, and rodent bait.

The biology of both beetles is nearly identical, and they are managed in the same manner so that it is not necessary to distinguish the two species. The adult beetles live an average of 6 to 10 months, but some individuals may live as long as 3 years. The female beetle of both species drops her eggs loosely among the foodstuffs or tucks them away in a crevice in a kernel of grain. When the small, slender, white eggs hatch, the emerging larvae crawl about actively, feeding here and there. They become fully grown in about 2 weeks during summer weather and then construct delicate cocoon like coverings by joining together small grains or fragments of foodstuff with a sticky secretion. Within this cell, the larva changes to the pupal stage. Development from egg to adult may take from 3 to 4 weeks in summer.

DRUGSTORE BEETLE (Stegobium paniceum)

Biology

• Length: About 1/10 inch

• Antennae have a 3 segmented club.

• Brown in color

• Superficially resembles the cigarette beetle

Distribution/Habits

• Will infest almost any household food and spice, as well as hair, leather and drugs.

• Will also infest books and manuscripts.

*Cigarette Beetle and Drugstore Beetle. The cigarette beetle and the drugstore beetle closely resemble one another, but the cigarette beetle is more common. Both beetles are about 1/8-inch long, cylindrical, and uniformly light brown. The easiest way to distinguish the two is by the wing covers: the wing covers of the drugstore beetle have longitudinal grooves, while those of the cigarette beetle are smooth.

Confused Flour Beetle and Red Flour Beetle.

The confused flour beetle and the red flour beetle are very similar in appearance and can be most easily distinguished by examining the antennae: the antennae of the red flour beetle end abruptly in a three-segmented club, while the confused flour beetle's antennae gradually enlarge towards the tip, ending in a four-segmented club. Adult beetles of these two species have shiny, reddish brown bodies that are about 1/7-inch long, flattened, and oval. These beetles have a very wide food range including cereals, damaged grains, grain products, shelled nuts, dried fruit, chocolate, drugs, and herbarium and museum specimens.

The biology of these two species are very similar; their average lifespan is about 1 year, but some have been known to live almost 4 years. The females lay their small, white eggs loosely in flour or other food material. The eggs, which are coated with a sticky secretion, become covered with flour or meal and readily adhere to the sides of sacks, boxes, and other containers. They hatch into small wormlike larvae that are slender, cylindrical, and wiry in appearance. When fully grown, the larva is 3/16-inch long and white, tinged with yellow. At this stage, it transforms into a small pupa. At first white, the pupa gradually changes to yellow and then brown, and shortly afterward transforms into a beetle. In summer, the period from egg to adult averages about 6 weeks.