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.
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Dorsal View
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Lateral View
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Pygidium
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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.