Southern Cowpea Weevil

Pronunciation

How to pronounce Callosobruchus chinensis: /kəˌloʊsoʊˈbrʊkəs tʃaɪˈnɛnsɪs/

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Summary

Callosobruchus chinensis, known as the Southern Cowpea Weevil or Adzuki Bean Weevil, is a small beetle that has become a major pest of stored legumes worldwide. Its lifecycle and behavior impact agriculture significantly, especially in regions reliant on pulse crops.

Physical Characteristics

C. chinensis is a small beetle, measuring about 2.7–5 mm in length as an adult. The adults are brown with black and grey patches, and exhibit sexual dimorphism where females are larger and heavier than males. The larvae are yellowish-white, and pupae are dark brown. Two morphologies exist: flight forms with lighter colored, larger bodies, and flightless forms that are darker and smaller.

Identification Tips

C. chinensis lacks the snout characteristic of true weevils, differentiating it from similar species. Females have slightly longer abdomens than elytra, which are white with two oval black spots. Males and females have different antenna structures, with males having pectinate (narrow) antennas and females having serrate (thicker and notched) antennas.

Habitat

C. chinensis prefers habitats within the tropics, particularly on plants within the Fabaceae family, such as green gram and chickpeas. They are typically found in stored pulses and legumes.

Distribution

Originally native to the tropics and subtropics of Asia, C. chinensis has become cosmopolitan due to international trade of legumes, being recorded across the US and Canada, albeit rarely surviving in the wild in Canada.

Diet

Both larvae and adults feed on legumes, including green gram, lentils, cowpeas, pigeon peas, chickpeas, and split peas.

Life Cycle

The complete life cycle ranges from 29 to 39 days, including egg incubation (4-6 days), larval development (12-20 days), pupation (7-10 days), and adult longevity (7-20 days).

Reproduction

Females can lay up to 90 eggs after one fertilization, typically laying one egg per seed. They may lay multiple eggs on a seed when resources are scarce but usually aim to reduce competition among larvae.

Predators

C. chinensis is subject to predation by various parasites, including parasitic wasps (e.g., A. calandrae) and mites. These can efficiently reduce their populations in storage facilities.

Ecosystem Role

C. chinensis is a key pest in the legume industry, impacting the storage and quality of pulses, thus playing a significant role in the ecosystem as a crop pest that affects agricultural practices.

Economic Impact

C. chinensis is considered one of the most damaging crop pests to stored legumes, causing significant economic losses due to damage in storage facilities.

Collecting Methods

• Manual collection from infested beans
• Trap barriers with specific lures
• Pheromone traps in storage areas

Preservation Methods

• Desiccation using silica gel
• Freezing to kill larvae and adults
• Using inert gases to displace oxygen in storage

Evolution

C. chinensis exhibits reproductive interference with congeneric species C. maculatus, affecting their reproductive behaviors and fitness through competitive mating.

Similar Taxa

• Callosobruchus maculatus

Misconceptions

While commonly referred to as the cowpea weevil, C. chinensis is not a true weevil but rather a member of the leaf beetle family Chrysomelidae.

Tags

• pest
• agriculture
• beetle
• legume pest