Scientific Name: Zabrotes subfasciatus (Boheman)

Common Names: Mexican bean weevil

Synonyms

Spermophagus musculus Boheman

Spermophagus pectoralis Sharp

Spermophagus semifasciatus Boheman

Spermophagus subfasciatus Boheman

Zabrotes pectoralis (Sharp)

Taxonomic Position

Class: Insecta

Order: Coleoptera

Family: Bruchidae

Genus: Zabrotes

Species: Zabrotes subfasciatus

Geographical Distribution

Asia – India, Israel, Lebanon, Myanmar

Africa – Ethiopia, Ghana, Kenya, Medagascar, Malawi, Mauritius, Nigeria, South Africa, Tanzania, Uganda

North America – Mexico, USA, Minnesota, Texas

Central America and Caribbean – Cuba, Guatemala, Honduras, Jamaica, Nicaragua, Panama

South America – Argentina, Brazil, Ecuador, Peru, Venezuela

Host Range

Cassia fistula (Indian laburnum),    Phaseolus (beans), Phaseolus acutifolius (tepary bean),      Phaseolus lunatus (lima bean), Phaseolus vulgaris (common bean), Triticum aestivum (wheat), Vigna (cowpea), Vigna mungo (black gram), Vigna radiata (mung bean), Vigna unguiculata (cowpea), Voandzeia subterranea (bambara groundnut)   

Pest Destructive Stage

Primary pest

Eggs –laid or stuck individually onto seed or pod

Larvae – immobile, concealed within seed

Adults – do not feed on commodity, fly readily

Damage Symptoms

In the early stages of attack by Z. subfasciatus, the only symptoms are the presence of the eggs cemented to the surface of the beans. Because larval and pupal development occurs entirely within the bean, the immature stages are not normally seen. The adults emerge through 'windows' in the grain, leaving round holes that are the main evidence of damage.

Identification Features

Eggs

The eggs of Z. subfasciatus are hemispherical. The female sticks them to the testa of a bean or to a pod. The eggs are oval, white, transparent, convex above, 0.5 x 0.4 mm.

Larvae

The larvae are normally only found in cells bored into beans. The larvae are white, scarabaeiform (a term used to describe the body shape of insect larvae that are shaped like the letter C), slightly curved. Head bearing one pair of ocelli. Thoracic legs become rudimentary.

Pupae

Also usually found only in cells bored into beans. Cox (1996) described and illustrated the pupa. It is about 3.0 mm in length and creamy white. The apical abdominal segment bearing few short dorsal setae, urogomphi absent. Spiracles present on mesothorax and abdominal segments 1 to 6.

Adults

• In adult Z. subfasciatus, the elytra are short, relatively broad and together are somewhat square in shape.
• The elytra of the female are strongly marked with a pattern of white and pale grey setae on a dark (almost black) background. The male has rather uniform light grey-brown pubescence (sometimes mottled with darker brown) over a dark-grey cuticle.
• On the apex of the tibia of each hind leg there are two movable spurs, called calcaria; these are reddish in colour and equal in length. There are no teeth on the hind femur.
• The tenth stria of each elytron is about half as long as the elytron.
• The front coxae are contiguous and not separated from each other by a ventral process.
• The body length ranges from 1.8 to 2.8 mm.
• Morphologically distinct forms of Z. subfasciatus can occur.

Detection methods

Samples can be examined with naked eye or under magnifying glass or stereoscopic binocular microscope and by using soft X-ray and seed transparency method hidden infestation can be detected.