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Michigan State University Extension
Home Maintenance And Repair - 01500524
06/24/03

Grain and Bean Weevils



Several types of weevils, including the rice, granary, maize and bean/pea weevils, can be encountered in the home. They are all pests of whole grain foods such as nuts, beans, cereals, fruits and seeds.

The true weevils (rice, granary and maize weevils) have a long snout on the head. The rice weevil is about 3 mm long dark reddish brown, with four pale spots on the upper surface. The rice weevil can fly and is attracted to lights. The granary weevil is slightly larger (4 mm), of the same body style and entirely dark chestnut-brown. It cannot fly and is not attracted to lights. The maize weevil is also slightly larger than the rice weevil, and it is very dark reddish-brown or black with four yellowish spots. All of these weevils infest whole grain rice, barley, corn, wheat, popcorn, sunflower seeds, nuts, beans and bird seed. They will also attack hard cereal products such as macaroni, dry pet food, cereals and caked flour.

The larvae are white, legless, and feed inside of the whole kernel or seed - hence they are rarely seen. Weevil damaged grains typically are hollow and have small, round emergence holes. The life cycle requires about 4 weeks and there may be three to five generations per year.

The bean weevils are not true weevils; they are members of the closely related bean weevil family. Their body shape is more round than the rice, granary and maize weevils and they do not have the slender protruding snout of these true weevils. The common bean weevil is about 1/8 inch (3 mm) long with the upper surface mottled shades of gray. These feed on dried beans, leaving perfectly round holes in the beans.

Very often, beans are harvested from the garden which look perfectly good. However, there can be been weevil larvae present inside. These larvae can continue to develop while the beans are in storage, with adults emerging during winter. Many a housekeeper has been dismayed to find a good supply of beans ruined by this insect. Heating the beans to 130 degrees F for 1/2 hour prior to storage will kill any larvae present and arrest any further development. A small number of dried larvae in the beans does not constitute any hazard to health.

Integrated Pantry Weevil Management

Purchase susceptible foodstuffs in quantities that can be used in a short time: 2-4 months, if possible. When purchasing packaged food, be certain the containers are not broken or unsealed and that there are no signs of infestation. Check the packages for freshness dates. Once 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 insect development. Keep food storage and preparation areas clean at all times; spilled and exposed food attracts insects.

If granary, rice or maize weevils are found in the kitchen, a search of all possible food sources should uncover the source of infestation. Disposal of infested grains and a thorough cleanup of the area should eliminate them.

For bean weevil control, all that is required is to remove the infested beans and clean up the storage area. This pest does not infest as wide a range of stored goods and an insecticide is not recommended.

For a complete listing of suggested control options for all home, yard and garden insect pests contact your local Extension Service, found under local government in the phone book.

References

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

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This information is for educational purposes only. References to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned. This information becomes public property upon publication and may be printed verbatim with credit to MSU Extension. Reprinting cannot be used to endorse or advertise a commercial product or company.

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 .