Flowers and Garden Home Seed weevils occasionally become pests of stored beans, cowpeas, and peas.  
Learn about the different insects and pests that affect gardens, lawns and food crops, and how to deal with them.
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Browse Articles: Insects and Pests
Seed Weevils
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Reference: Ohio State University Extension

Common Name Scientific Name
Bean WeevilAcanthoscelides obtectus (Say)
Cowpea WeevilCallosobruchus maculatus (Fabricius)
Pea WeevilBruchus pisorum (Linnaeus)

Seed weevils occasionally become pests of stored beans, cowpeas, and peas. Damage consists of complete or partial destruction of infested seeds by numerous round holes or destruction of all but the outer shell. Many bean weevils may develop from a single seed and later be discovered on windows and doors. They do not bite or sting humans or pets, spread disease, or feed on or damage the house or furniture.

Identification
Seed weevils are oval-like, have a triangular pronotum (top plate-like segment on middle body part), small head, 11-segmented antennae arising in front of the eyes, and shortened wing covers exposing the tip of the abdomen. They are less than 3/4-inch long and are covered with short hairs or scales that are brown, gray, black, or a combination of these colors. Larvae are white, curved, thick-bodied, wrinkled, about 1/8-inch long at maturity, and feed inside the seeds. Eggs are oval and white.

Adult bean weevils are light olive brown, thickly covered with darker brown, grayish-yellow hairs, but with dark cross bands on the wing covers. They are about 1/8-inch in length with reddish-brown legs and black antennae. The body narrows evenly toward the small head.

Bean Weevil
Bean Weevil

The cowpea weevil has wing covers with a large rounded spot at midlength and the tips are black. Pea weevils are blackish and covered with reddish-brown and white hairs. They are about 3/16-inch long, with a whitish abdomen end and black legs.

Pea Weevil: adult and larva
Pea Weevil: adult and larva

Life Cycle and Habits
The life cycle of seed weevils may be completed in 21 to 80 days, depending on the temperature. If seeds are stored in a warm place, the bean weevil and cowpea weevil will breed continuously in dried seeds throughout the year. Bean weevils infest kidney beans, lima beans, and cowpeas in the field and all varieties of beans, peas, lentils, and certain other seeds in storage. Adults do not feed on the beans, but may fly to windows and doors to escape. They often feign death. Females lay white eggs on pod beans in the field or on beans in storage, and larvae emerge in 5 to 20 days. Tiny legless grubs enter the beans and eat out a cavity, becoming mature in 11 to 42 days. They pupate in the beans for 5 to 18 days and, when adults emerge, they cut round holes 1/10-inch in diameter through the seed and crawl out. Usually one to two generations are produced in the field each year and six or more generations are produced in storage each year. The pea weevil attacks peas only in the field and does not lay eggs on dried seeds. Under heavy infestations, as many as a dozen or more weevils may develop from a single seed. When a pair of bean weevils were placed in a bag containing 87 pounds of red kidney beans, 250,000 adults were produced in 14 months.

Control Measures
The homeowner frequently sees seed weevils for the first time on windows and doors as they emerge from stored seeds, are attracted to light, and attempt to escape. Usually, there is little concern for their presence until a sack of dried beans or peas, especially homegrown, is emptied and found full of holes.

Prevention
The simplest and most effective prevention 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. As soon as seed weevils are correctly identified, they can then be quickly discovered in stored beans or peas. Other foods, such as cereals, cornmeal, flour, nuts, grains, pet food, birdseed, etc. will not be infested by the bean weevil. If practical and regulations permit, wrap infested foods securely in heavy grocery bags and discard in a dumpster to be taken to a sanitary landfill. Also, if permitted, burning or burying infested seeds can be effective.

Apply control measures soon after harvest and before storage. Examine seeds carefully at the time of purchase or harvest. Homegrown beans and peas are first infested in the garden or field before harvest and storage. Store only clean, dry seeds with a moisture content of 12 percent or less to reduce damage. All insect life stages can be killed by super-cooling in a deep freeze at 0 degrees F for 4 days, cold storage at 32 degrees F for 58 days, or super-heating in an oven at 145 degrees F for 2 hours or in a microwave oven for 5 minutes. However, seeds saved for planting may have the germination reduced by super-cooling, super-heating, or microwave methods. After treatment, seeds should be stored in containers of glass, heavy plastic, or metal with screw-type, airtight lids. Refrigeration or deep freeze storage is helpful.

Storage of grains for a month or more during the warm summer months may lead to infestations. Purchase in small quantities for early use.

Insecticides
The use of insecticides is discouraged around food materials. Insecticides are supplementary to sanitation and proper storage. Household insecticides have no effect on insects within food packages. For extra protection, some treat seeds or grains before storage with dusts or sprays of pyrethrin, labeled for this use. (Follow label directions and safety precautions.) If the problem becomes severe and widespread, contact a reputable, licensed pest control operator who has the training, experience, equipment, and insecticides to get the control job accomplished safely.

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  Data Source: Ohio State University Extension. Articles and resource may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide and it is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used.