Sawtoothed & Merchant Grain Beetle

Sawtoothed & Merchant Grain Beetle, Oryzaephilus surinamensis (L.), is a widely distributed species commonly found in stored grain. It is often confused with a closely related species, the less common merchant grain beetle.

Adults are 2.5 mm long. The body is very flat and is well adapted for crawling into cracks and crevices. They are very easily identified. The margins of the thorax are saw-like and posses six projections on each side. In addition, there are three longitudinal ridges on the top surface of the thorax. A tooth on the femur of the hind leg separates the male from the female.

Wings are well developed but there is no record of this insect flying. A related species, the merchant grain beetle (0. mercator (Fauvel)), can fly and is more often found in warmer climates. To separate these two beetles, you need to examine the head for a small projection behind the eyes. On sawtoothed grain beetles the projections are curved and wide.

whereas on the merchant grain beetle the projections are pointed and narrow. Sawtoothed grain beetle larvae are a yellowish white except for their head, which is brown. Full-grown larvae are less than 3 mm (1/8 inch).

This beetle can be found feeding on cereals, fried fruit, bran, rolled oats, brown rice walnuts, breakfast foods, macaroni, sugar, drugs, fried meats, chocolate, tobacco, and snuff. It cannot attack perfectly sound grain, but can feed on slightly damaged grain. Thus, it is often found in whole grain in association with other insects. It has been observed feeding on eggs and dead adults of stored-product moths.

Life Cycle : The habits and development of the two species are similar. The merchant grain beetle, however, is less cold tolerant and lays only about one-half to two-thirds as many eggs as does the sawtoothed grain beetle. The adult merchant grain beetles are strong fliers and may originate from other areas; they also are introduced into new grain from contaminated grain. The adults of the sawtoothed grain beetle, on the other hand, cannot fly and must be introduced from contaminated grain.

Adults live an average of six to ten months, but can live as long as three years. The females lay between 43 and 285 eggs during their lifetime. Eggs are dropped loosely among grain kernels or tucked into a crevice in a kernel. The tiny eggs are slender and white, and hatch in three to five days when environmental conditions.

The larvae emerge and crawl freely about the grain to feed on broken kernels. Larger larvae may tunnel into kernels to feed. Larvae mature in about two weeks, and construct cocoon-like coverings by joining together small grains or pieces of grain. Within these structures the larvae pupate. the pupal stage lasts about a week. Total development from egg to adult requires about three to four weeks.

Damage : Although broken kernels are the preferred food of both species, sound kernels will sometimes be penetrated and fed on. The dry weight of grain may be reduced, but total weight may increase because of water absorption caused by the metabolic processes of insect populations. Molds may begin to grow on the gain, further reducing grain quality and value. The presence of live insects and/or insect parts can also result in reduction of grain value. In some cases, grain can be rejected at the terminal.

Control: The simplest and most effective control measure is to locate the source of infestation and quickly get rid of it. Use a flashlight or other light source to examine all food storage areas and food products carefully. Dispose of heavily infested foods in wrapped, heavy plastic bags or in sealed containers for garbage disposal service, or bury deep in the soil if permitted, practical, and regulations allow. If you detect infestations early, disposal alone may solve the problem.

Time of purchase, carefully examine foods, such as flour, pancake flour, cornmeal, cereals, raisins, dry dog and cat food, spices, candy, dates, dried meats and fruits, rice, and macaroni. Check the packaging date to establish freshness. Examine broken and damaged packages and boxes to avoid bringing these stored-product pests accidentally into the home. Purchase seldom-used foods in small quantities to prevent long storage periods of one month or more, especially during the warm summer months. Store susceptible foods in insect-proof containers of glass, heavy plastic, or metal, ideally with screw-type lids, or store in a refrigerator or freezer. Use older packages before newer ones, avoid spillage in cabinets, and always keep food storage spaces clean. Properly ventilate the storage area to discourage these moisture-loving stored-product pests.

Lightly infested or suspect foods with questionable infestations can be heated in a shallow pan in the oven at 120 degrees F for 1 hour or at 130 degrees F for 30 minutes, placed in a deep freeze at 0 degrees F for 4 days, or heated in a microwave oven for 5 minutes. Heat-treat dried fruits or vegetables by placing in a cheesecloth bag and dipping in boiling water for 6 to 10 seconds. Sifting the food material will remove insect fragments. Any remaining fragments will not cause harm if consumed. After insects are killed, contaminated food might be used outdoors, during the winter months, for bird feed. Seeds saved for planting may have the germination reduced by super-heating or cooling.

Careful sanitation is the best method to avoid stored-product pests. After removing all food, food packages, utensils, dishes, etc. from the cupboard, shelves, or storage area, use a strong suction vacuum cleaner with proper attachments to clean all spilled foods (cornmeal, toaster crumbs, bits of pet food, raisins, etc.) from the cracks and crevices, behind, under, and in appliances and furniture. Scrub with soap and hot water. After shelves are thoroughly dry, cover with clean, fresh paper or foil before replacing food or cooking utensils. The ability of these insects to find a small amount of food is amazing.

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