Home-stored product entomology is the study of insects that infest foodstuffs stored in the home. It deals with the prevention, detection and eradication of pests. This field is related to forensic entomology, as consumers who find contaminated products may choose to take legal action against the producers. Suitably qualified entomologists are likely to be able to determine the identity of contaminant species, even when no insects are found and the only evidence of infestation is the resulting damage. They should also be able to determine whether the foodstuff was contaminated before or after purchase, to determine whether the producer (rather than the consumer) is at fault.
Major stored product pests
Flour beetles (Tribolium castaneum and Tribolium confusum)
Two different types of beetles are classified as flour beetles: the red flour beetle and the confused flour beetle, which have similar physical characteristics. They are flat and oval in shape and usually range around 1⁄8 inch (3.2 mm) long. Their exoskeletons are reddish brown with a shiny and smooth texture. In both species, the eggs are white or colorless. They are very small in size and have a sticky outer covering that causes certain food particles to stick to them. The larvae have six legs, with two pointy projections toward the caudal end. Finally, the pupal stage (a cocoon-like form) is usually a white or brownish color. The beetle life cycle lasts about three years or more, with the larval stage ranging anywhere from 20 to over 100 days, and the pupal stage around eight days. Beetles usually breed in damaged grain, grain dust, high-moisture wheat kernels, and flour. The female flour beetle can lay between 300 and 400 eggs during her lifetime [a period of 5 to 8 months]. The flour beetles mainly infest grains, including, but not limited to: cereal, corn-meal, oats, rice, flour, and crackers. This type of beetle is the most abundant insect pest in flour mills across the United States. Their small size allows them to maneuver through cracks and crevices and get into the home and other areas. Once they are present in areas with potential food sources, they can infest material such as flour, resulting in a sharp odor or moldy flavor. The red flour beetle can fly short distances and the confused flour beetle is unable to fly. While the confused flour beetle is more commonly found in the northern United States, the red flour beetles are more predominant in the southern United States in areas with warmer climates.
The red flour beetle and the confused flour beetle are commonly used as model organisms, to study genetics and ecology. The genome of the red flour beetle has been sequenced.
Drugstore beetle (Stegobium paniceum)
This beetle is related to the commonly known cigarette beetle. Adult drugstore beetles are cylindrical with lengths ranging from 2.25 to 3.5 millimetres (11⁄128 to 9⁄64 in). They are a reddish-brown color and have elytra, sclerotized (hardened) wings that fold back over the abdomen and hinge upwards, allowing the hind wings to come out to fly. Females are capable of laying up to 75 eggs during a 13- to 65-day period. After the eggs are laid, they hatch into a larval period that can range anywhere from four to 20 weeks. After the larval period, drugstore beetle larvae move out of the substrate to build a cocoon and pupate. The pupation period takes a total of 12–18 days. The entire life cycle of the drugstore beetle lasts approximately two months but can be as long as seven months. These stored product pests will infest almost anything readily available. Food products prone to infestation include flour, dry mixes, breads, cookies, and other spices. Nonfood materials include wool, hair, leather, and museum specimens. This specific type of beetle has symbiotic yeasts that produce B vitamins, which allow the beetle to survive even when consuming foods of low nutritional value. They are found in areas that have a warmer climate, yet are less plentiful in the tropics than the cigarette beetle.
Sawtoothed grain beetle (Oryzaephilus surinamensis)
The sawtoothed grain beetle is closely related to the merchant grain beetle, and is commonly found in kitchen cabinets feeding on items such as cereal, breakfast foods, dried fruits, macaroni, crackers, etc. They are the most common grain and stored product pest in the United States. They are very active and tend to crawl rapidly while searching for food. They are small insects, reaching a length of about 1⁄8 of an inch. Their name originates from their distinguishable, sawtooth-like projections found on each side of the thorax. The body of the beetle is flat and slender in shape, and brown in color. The size and shape of the mandibles allow the beetles to easily break through well-sealed packaged foods. An adult female can lay between 45 and 250 eggs that usually hatch within three to 17 days. The larvae have a caterpillar-like appearance, with a yellowish coloration to the body and a brown head. The larval period can last as long as 10 weeks but can be as short as two weeks. Following the larval instars is the pupal period, which can last one to three weeks. The pupal stage is characterized by the unique process by which these beetles stick together pieces of food material to form protective coverings around their bodies. A fully mature adult beetle, under optimal conditions, can live a maximum of four years, a long lifespan for an arthropod.
Indianmeal moth (Plodia interpunctella)
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