Insect identification > Coleoptera > True Coleoptera > Bean weevil

Bean weevil

The bean weevil (Acanthoscelides obtectus Say). - This insect is now found in nearly all parts of the world. The beetle is smaller than the pea weevil and is brownish-gray in color, its elytra slightly mottled.

The beetle lays its eggs on or in the pods of the beans growing in the field, either in holes it makes or in cracks caused by the pods' splitting. In the case of shelled beans the eggs are placed on the beans themselves.

The larvae gnaw their way to and into the beans, and unlike the pea weevil a number may enter the same seed and feed upon its substance. Development from the egg to the adult occurs within the bean and the adult finally escapes through a circular hole it has cut in the skin after having spent from 3 weeks to nearly 3 months there, according to the temperature where the beans are kept.

When infested beans gathered in the field are brought in, their infestation may not be apparent, but, after they are kept a while, the adult beetles will escape and lay their eggs for another generation which will develop in the same seeds if these are kept where it is fairly warm , and thus by spring there may be practically no beans left to plant.

Six generations may be produced in a year in the South and, if the beans are kept where it is warm during the colder months, as many may occur in northern localities, though in the field it is doubtful if there are more than one or two.

Another species, the cowpea weevil (Callosobruchus chinensis L.), which feeds on the cowpea and other peas and beans, is more abundant in the South, and a fourth, the four-spotted bean or cowpea weevil (Bruchus quadrimaculatus Fab.) has a wide distribution, probably wherever cowpeas are grown. Both of these species breed generation after generation in stored cowpeas, and in warm temperatures there may be a number of generations each year.