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Agriculture >> Resources >> Plant and Disease Identification

Agriculture

Plant and Disease Identification

Bean Weevil
Acanthoscelides obtectus (Say)

Injury

The bean weevil is a pest of stored beans and peas throughout the United States and in many other countries. This insect belongs to the beetle family Bruchidae (commonly known as the seed weevils because the larvae develop inside the seeds of various plants). Occasionally one may take a package of dried beans or peas out of the closet only to find it infested with the bean weevil, or, weevils may be noticed when they try to escape through the window. Dead weevils may accumulate on the sills.

In the field, kidney beans, lima beans and cowpeas are attacked. In storage, all varieties of beans, peas, lentils and some seeds are attacked. The larvae feed inside the beans and when numerous, nothing but the shell remains. This reduces the food value of the beans as well as reducing the germination potential of the bean seed.

Description

The adult bean weevil is a short chunky beetle, about 1/8-inch in length and in general, olive brown with darker brown and gray patches on the wing covers. The elytra are shorter than the abdomen leaving a few segments exposed. The larva is a white grub with a brown head. It is about 1/8-inch long at maturity and has a wrinkled, humpbacked appearance.

Life History

Adult weevils lay eggs on the developing bean pods in the field. In 3 to 30 days the tiny grubs emerge and make their way into the seed. Here they feed until mature, and pupation occurs. When the adults are ready to emerge, they cut round holes (1/l0-inch in diameter) through the seed coat and crawl out.

Indoors, in stored seed, multiple generations occur and breeding continues as long as there is any food left in the beans and the temperature is suitable for reproduction.

Management

Often infestation is not noticed when the beans are harvested. Bean seed used for cooking purposes is dry when harvested. Shells are then removed. The time to take action is right after the dry beans are harvested. Either freezing or oven heating can control the weevils.

Beans or peas should be placed in a freezer at 0°F. or less for four days. The beans may be stored in the freezer if space permits, or they may be stored in glass jars or metal containers. Be sure the beans are dry before storing in containers as moisture may cause molds or other spoilage.

For oven heating, either a gas or electric stove may be used. Place the beans in a shallow pan, less than two inches deep, and turn on the oven.

• For gas ovens -- turn the heat on as low as it will burn well for about 15 minutes. The center of the beans should reach 120° degrees F and the outer temperature should be about 180° F. Turn off the heat and leave the beans in the warm oven for 1/2 hour.
• With an electric oven, turn the heat on low and heat until the center of the beans reaches 120° F. This should take about 1/2 hour also. This temperature will not injure the beans or peas.
• After treatment, the beans may be stored in containers with tight fitting lids where they will remain free from infestation.

3/1976 Prepared by Carolyn Klass, Sr. Extension Associate
Dept. of Entomology, Cornell University

5/1986 Revised

Every effort has been made to provide correct, complete, and up-to-date pest management information for New York State. Changes in pesticide regulations occur constantly, and human errors are still possible. These recommendations are not a substitute for pesticide labeling. Read the label before applying any pesticide. Trade names used herein are for convenience only. No endorsement of products is intended, nor is criticism of unnamed products implied.

Cornell Cooperative Extension and its employees assume no liability for the effectiveness or results of any chemicals for pesticide usage. No endorsement of products is made or implied.

**HOME REMEDIES: These remedies are not endorsements by Cornell University of any product or procedure. They are not recommendations for use either express or implied. Neither Cornell University, nor its employees or agents, are responsible for any injury or damage to person or property arising from the use of this information.