Species Spotlight - The Cowpea Weevil (Callosobruchus maculatus)

Ethan Estabrook, BCE - Research Associate at Insects Limited

The cowpea weevil (Callosobruchus maculatus) is a stored product insect pest that infests and feeds on stored legumes, such as cowpeas (black-eyed peas), chickpeas, lentils, mung beans, adzuki beans, and dried peas.

Although weevil-like, cowpea weevils are not true weevils. They belong to the bean weevil and seed beetle subfamily Bruchinae which is now a part of the leaf beetle family Chrysomelidae.

Adults are small (3-4mm long) with long legs and long antennae. They have mottled reddish-brown coloration with two blackish spots on the wing covers.

Their wing covers do not completely cover their abdomen leaving parts exposed.

Adults do not feed and are short-lived living for 10-14 days. A female cowpea weevil can lay around 100 eggs on the surface of beans which hatch in about 4-8 days.

Emerged larvae will burrow into a legume to feed and develop from within.

After a week or two, the cowpea weevil will emerge out of the legume as an adult completing their life cycle in as little as 21 days.

Male cowpea weevil (Callosobruchus maculatus) (left) and female cowpea weevil (right). Notice the difference between the body shape and antenna length.

Unlike other stored product insects, cowpea weevil adults can be found in two morphological forms: one with wings and capable of flight and the other without wings and flightless. The flightless form is common while food and environmental conditions are optimal. As conditions become more unsuitable, such as from high larval density or high temperatures, the winged form becomes more common. This morphological change may help facilitate cowpea weevil dispersion to more suitable areas such as growing seeds in the field.

Cowpea weevil (Callosobruchus maculatus) damage to chickpeas.

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