Cowpea Weevil

Pronunciation

How to pronounce Callosobruchus maculatus: //kəˌloʊsoʊˈbruːkəs ˌmækjuˈleɪtəs//

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Summary

Callosobruchus maculatus, commonly known as the cowpea weevil, is a significant pest of stored legumes, originally from Africa. It is associated with a high degree of inbreeding and exhibits unique reproductive behaviors among its species, strongly influencing its pest status globally.

Physical Characteristics

2.7–3.0 mm in size, reddish-brown overall with black and gray elytra marked with two central black spots. The last segment of the abdomen extends out from under the short elytra, also with two black spots. The cowpea weevil lacks the 'snout' of a true weevil and is more elongated in shape. It is sexually dimorphic, with females being darker overall, while males are brown.

Identification Tips

Distinguished from other species of Callosobruchus by its morphological traits and coloration. Females are usually darker and sometimes larger than males, and the plate covering the end of the abdomen is large and dark in females but smaller in males.

Habitat

Typically found in legume storage areas where temperature and humidity are relatively constant; lays eggs on legumes both in the field and in storage.

Distribution

Cosmopolitan distribution, most likely of African origin, adventive in the southern United States, and present on every continent except Antarctica.

Diet

Attacks cowpeas and various beans in storage, including Cajanus cajan, Cicer arietinum, Glycine max, Lablab purpureus, Lathyrus spp., Lens culinaris, Phaseolus spp., Pisum sativum arvense, Vicia spp., and Vigna spp.

Life Cycle

A female can lay over a hundred eggs; larvae emerge 4 to 8 days later and feed inside the bean for 3 to 7 weeks before maturing. Lifespan of adults varies between 10 days to 4 weeks depending on conditions, with larval crowding affecting development time.

Reproduction

Mating involves copulation that can injure the female due to the male's penile spines. Females lay single eggs on beans, and reproductive strategies vary based on host availability and nutrient sources.

Predators

Predators include several parasitoid wasps such as Anisopteromalus calandrae, Uscana mukerjii, and Dinarmus wasps, which target the larval and egg stages.

Ecosystem Role

Major pest of stored legumes, causing significant post-harvest losses.

Economic Impact

Considered one of the most well-known and universally destructive members of the Bruchidae, it poses a significant threat to legume crops.

Health Concerns

Medically harmless to humans; considered an agricultural pest.

Evolution

Likely underwent multiple bottlenecks due to small populations moving with legume trade; persisting despite high degrees of inbreeding.

Similar Taxa

• Callosobruchus chinensis

Misconceptions

Often mistaken for true weevils due to its common name, but it is not a true weevil and belongs to the leaf beetle family Chrysomelidae.

Tags

• cowpea weevil
• Callosobruchus maculatus
• pest
• legume beetle
• agricultural pest