Fact Sheet FS1383
Figure 1: A bean weevil on the bean pod.
An Introduction to Bean Weevils
Bean weevils (Acanthoscelides obtectus) are significant pests of stored beans, peas, lentils, and other legumes, affecting both home pantries and garden harvests. First described in the United States in 1831 by naturalist Thomas Say, they have since become an economically and agriculturally important pest of stored legumes. Likely originating in Mesoamerica or northern South America, bean weevils have spread worldwide through the trade of bean seeds and are now found on every continent except Antarctica. Infestations from these beetles can cause extensive damage to bean crops in the field and to stored beans, with losses reaching 40–50% of the product.
General Biology and Life History
Bean weevils are not true weevils because they lack the characteristic snout of true weevils. They are also known as seed beetles, and belong to the leaf beetle family, Chrysomelidae. These beetles have four stages in their life cycle: egg, larva, pupa, and adult. Eggs are small, about 1/40 inches in length, milky white in color, oval-elongate in shape, and wrinkled. Larvae initially have legs but lose them once they mature after the first molt and are about 1/8 inch long. Pupae are white, then later, a yellowish color. Adult bean weevils can fly, and their wing covers are mottled brown-black and gray in color. The adults are about 1/10 to 1/8 inches in length.
Figure 2: Larval bean weevil (left) and adult (right). Photographer: L.J. Buss, University of Florida.
After mating, female bean weevils will lay dozens of eggs, typically on or around the seeds or pods, or within the seeds themselves. The eggs hatch in about 20 to 30 days. It is common for storage pests to produce only one larva per seed, but for this species, multiple larvae may emerge from one seed. Larvae bore into the seeds where they will feed and then further develop into pupae in around 2 to 6 weeks. Pupae will then emerge as adults from the seed pod via a neat circular exit hole they cut through the seed. Adults do not eat the seeds; instead, they will mate and look for more seeds to infest. Adults are also short-lived.
If the temperature is suitable, within storage, multiple generations can occur if there remains a food supply within the container. Outdoors, they will search for other bean plants to infest. The entire life cycle takes about 30 days under optimal conditions and 90 days under cooler temperatures. There are typically around 6 to 8 generations produced per year. It has not been established whether the bean weevil can overwinter outdoors as available evidence indicates that they do not survive well under freezing temperatures, although they are cold-tolerant.
Evidence in the Home
Figure 3: Riddled bean - Bean weevil.
An infestation may be difficult to detect, as seeds that are currently infested with larvae may show no external signs of damage or infestation. Holes within the seed will only be visible once the larvae have completed their development into pupae and have exited the seeds, which will be apparent on harvested beans. Adults, if indoors, may be found congregating in large groups around windowsills or crawling on the walls. Dead adult bean weevils may also be visible around the seeds or plants.
Management
When growing legumes in the garden, it is important to be cautious when planting seeds, as the seeds may already be infested without any visible indication. Avoid planting any leftover seed from the previous year and always keep seed stored in a sealed, airtight container. Storing seeds indoors or in warm temperatures may result in insect survival if they are already infested. Dry store-bought beans may also contain larvae and should be treated before being placed in long-term storage.
To treat potentially infested seed, place beans or other legumes in dry heat at 130 °F for 4 to 5 hours. Beans must remain in the heat long enough for it to penetrate through the seed to kill the larva. Alternatively, beans could be placed in cold storage at 23 °F within the freezer for 21 days. Refrigeration is not an adequate method to completely kill the insect. Notably, at -19 °F, all stages are killed. Both methods mentioned may negatively impact seed germination. Insecticides are not recommended for the management of this insect.
More to Know
Bean weevils are interesting in that they feign death, like opossums, when disturbed and will drop off the plant. Additionally, these insects produce a sweet and fruity pheromone, most noticeable when they are cultured. They have also been known to use fungi as a nutritional resource and a reproductive site. Researchers are currently developing many new ways to manage these pests. It has been found that bean weevil resistance in beans is genetic, via the identification of three genetic markers, and this may lead to the development of weevil-resistant bean plants. Additionally, the use of parasitoids, essential oils, diatoms, fungi, and inert powders are other areas of research being explored for management and prevention.
This fact sheet is based on the original work of Gerald M. Ghidiu, Extension Specialist Emeritus in Vegetable Entomology, Retired.
To get help with an insect or other horticulture issue you are facing in your garden or landscape, submit a request for support at Go.Rutgers.edu/GardenHelpline.
Please see FS1123, Vegetable Insect Control Recommendations for Home Gardens, for more information.
References
December 2025
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