Stored Grain Insects



Cowpea Weevil

Callosobruchus maculatus



Cow Pea weevil (Callosobruchus maculatus)
Courtesy of CSIRO Division of Entomology

The adult cowpea weevil (Callosobruchus maculatus) is a relatively small beetle, 3 - 4 mm in length, somewhat teardrop or triangular in shape, and dull-colored with white, reddish, or black markings.


Pupae (top) and Larvae of the Cowpea weevil

Life cycle
The eggs are glued to the bean or the pod. On hatching the larvae bores into the seed where it makes a translucent 'window' in the seed before pupating. The larval and pupal stages are spent inside the bean. The adult emerges through the 'window' leaving a neat round hole. Infestations can begin in the field. Adults move to bean fields from trash beans left in sacks, harvesters, planters, or feed areas. The cowpea weevil readily attacks dried beans; thus this weevil can be a serious storage pest. Bean weevil infestations can also start in the field and may also originate from trash beans. As with the cowpea weevil, bean weevil will attack dried beans and can be a serious pest in stored beans. Broad bean weevil infestations also start in the field, but this pest is not a storage problem.

Damage in legume seed by Cowpea weevil

The larval stage of the weevil tunnel and develop within the beans. They may consume nearly the entire bean contents. Pupation occurs in the beans and adults emerge through a round hole in the seed coat. Damage is a combination of the feeding and contamination.

Cowpea weevil

Sanitation offers the most practical means of control. Since field infestations originate from beans, potential sources of weevils should be eliminated in production areas. Potential sources of weevils include broken sacks of seed beans left over from planting; seed beans left in planting hoppers; cull beans used in animal feed programs in a production area; small collections of beans remaining on or in a harvester following harvest; and small piles of beans remaining in or around the field after harvest or in a warehouse area.