Bean Weevil

Pronunciation

How to pronounce Acanthoscelides obtectus: /əˌkænθoʊˈsɛlɪˌdez ɒbˈtɛktəs/

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Summary

Acanthoscelides obtectus, commonly known as the bean weevil, is a species of bruchid beetle that serves as a pest of legume seeds. Originating from northern South America, it has spread widely due to human activity, affecting agricultural practices.

Physical Characteristics

Small beetles ranging in size from 2 to 5 mm; color ranges from light to dark brown with longitudinal spots on elytra and a red posterior border; elytra does not cover the abdominal end; legs are yellow-red; antennae are red-brown; eggs are milky white; larvae are white with yellow heads in the first instar and white with brownish heads from the second instar, with bristles and three pairs of legs.

Identification Tips

Look for longitudinal spots on the elytra and a red posterior border; the head is bent forward, lacking the long snout characteristic of true weevils.

Habitat

Favours warmer climates, often found in association with leguminous plants, particularly in fields and storage facilities.

Distribution

Widely distributed in warm regions of Europe, Africa, parts of Asia, North and South America, and introduced globally through grain shipments; not found in Australia.

Diet

Primarily feeds on the seeds of common beans (Phaseolus) and Vigna; also feeds on seeds of peas, vetches, and some non-legumes like maize and buckwheat; larvae feed on seeds.

Life Cycle

Development takes 100 to 110 days; eggs take about 30 to 45 days to hatch; larvae feed for approximately 3 to 3.5 weeks before pupating inside the seed for 9 to 29 days.

Reproduction

Females lay 2 to 20 eggs on or within seed pods; a single female can lay up to 200 eggs, with an average fecundity of 40 eggs.

Predators

A number of parasitoid wasps target bean weevil larvae.

Ecosystem Role

Acts as a pest of legume seeds in both field and storage environments, potentially reducing crop yields significantly.

Economic Impact

Can reduce crop yields by up to 60% in infested crops, especially in non-native regions like Australia.

Evolution

Originally described as Bruchus obtectus by Thomas Say in 1831, later reclassified under Acanthoscelides; misidentified as Bruchus obsoletus in historical literature.

Misconceptions

Historical misidentification with the species Bruchus obsoletus, which belongs to another genus.

Tags

• Acanthoscelides obtectus
• bean weevil
• pest
• legume seeds
• bruchid beetle