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Michigan State University Extension
Home Maintenance And Repair - 01500523
06/24/03

Grain and Flour Beetles



There are three common beetles that infest stored grains, flour, cake mixes and other flour products. These are the saw-toothed grain beetle, the red flour beetle and the confused flour beetle. All life stages of these "bran bugs" can be found directly in the food they infest. Infestations are usually discovered when an infested package is opened for use, or when small brown beetles are discovered in the kitchen near containers of stored grain products.

The sawtoothed grain beetle is about 1/8" (3mm) long, dark brownish-red, and has six saw-like teeth on each side of the prothorax, the body segment behind the head. The larvae are very small (less than 1/4 inch), yellowish -white and worm-like. Both the beetles and larvae feed on flour, grains, cereals, shelled nuts, bread, dried fruits, macaroni, spices, candy, sugar and other stored products. The small size and flattened shape of the beetles enable them to enter poorly sealed packages.

The complete life cycle (egg to adult) may occur in 40 to 60 days. There may be up to six generations per year. The adults live for an average of 6-10 months but can live as long as 3 years.

The confused flour beetle and the red flour beetle, are serious pests of milled and processed grains, especially flour. They may also infest beans, peas, dried fruits, shelled nuts, chocolate, spices and tobacco. Adult flour beetles are small (1/7 inch), reddish-brown and have a smooth-sided thorax. They are shinier and more convex than the sawtooth grain beetles. The red and confused flour beetles look very similar, differing primarily in the shape of their antennae. The larvae are yellowish-white, worm-like, and have a two pointed structure on the tail end.

The life cycle (egg to adult) generally takes 6-8 weeks. There may be up to 5 generations per year. Adults generally live for a year.

A fourth grain beetle sometimes found in Michigan homes is the foreign grain beetle. It looks somewhat similar to the saw-toothed grain beetle, except it lacks the saw-teeth on the side of the prothorax. Surprisingly, this grain beetle is not usually found in stored grains. It is more commonly encountered feeding on molds growing on moist grain, and in new houses on new cabinets made of particle board. The particle board, when new, may still be damp and mold may grow on the plant materials used in its construction. These beetles can live on this and are often quite common around bathroom vanities and kitchen cupboards. So far, we have no seen this beetle infesting stored products, but given the proper conditions, it could do so.

Integrated Grain & Flour Beetle Management

Purchase susceptible foodstuffs in quantities that can be used in a short time: less than 2-4 months, if possible. When purchasing packaged food, be certain the containers are not broken or unsealed. Check the packages for freshness dates. Once the food is in the home, use older packages before newer ones, and opened ones before unopened ones. Storing dried foods in a freezer will prevent pest development. Keep food storage and preparation areas clean at all times; spilled and exposed food attracts insects.

(1) To control grain and flour beetles, start with a thorough check of all stored foodstuffs. Once the infested materials are found, discard any that are thoroughly infested. Check for open pet food bags for infestation. Check for open dry pet food, these can harbor the beetles.

(2) While all stages of these insects can be killed with heat (130 degrees for 30 minutes), the risk of releasing large numbers of insects during the heat treatment process makes this tactic questionable. The beetles can be killed in packages by placing the items in a freezer for 3-4 days. However, there is no easy way to separate the insects from the food once they are killed.

(3) Contents from all packages (opened or unopened) which appear to be uninfested should be transferred to glass or plastic containers with tight-fitting lids. It is possible that eggs were laid in these products and that they may hatch later and lead to an infestation if not contained. Boxes, plastic bags and paper bags cannot be sealed tightly enough to exclude these pests. Glass containers make periodic examination of the food easier.

(4) Remove all food, food containers and utensils from the infested areas and clean thoroughly, first with a vacuum cleaner and then with soapy water. Special attention should be paid to cracks, crevices and corners (including under and behind appliances) were bits of flour, meal or other food may have accumulated.

(5) We do not recommend using an insecticide.

(6) Continue to observe the area for several months after treatment. If beetles reappear, the cleanup may have been inadequate or infested packages may have been brought into the home.

For a complete listing of suggested control options for a for all home, yard and garden insect pests see: Michigan Insect Pest Management Guide, 1991.

Publication like this are available from your local Extension Service. Read and follow instructions on the pesticide label. Heed all warnings. Check with your physician if you have any concerns regarding your personal health risk.

References

Revised by Tom Ellis, M.S., Department of Entomology

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MSU is an affirmative-action, equal-opportunity employer. Michigan State University Extension programs and materials are open to all without regard to race, color, national origin, gender, gender identity, religion, age, height, weight, disability, political beliefs, sexual orientation, marital status, family status or veteran status. Issued in furtherance of MSU Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Thomas G. Coon, Director, MSU Extension, East Lansing,MI 48824. This information is for educational purposes only. Reference to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned.

This information.was reviewed as of June 2008.  For more information about the contents please contact costner@msu.edu for webpage problems strausc@msu.edu .