THE COLEOPTERA 



129 



The Common Bean Weevil (Bruchus 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 

 (Fig. ] 21). The beetle lays its eggs on or in the pods of the beans growing 

 in the field, either in holes made, 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. Devel- 

 opment 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 tempera- 

 ture where the beans are kept. When infested 

 beans gathered in the field are brought in, their 

 infestation may not be apparent, but after 

 being kept a while, the adult beetles will escape 



Fig. 121. Fig. 122. 



Fig. 121. — Adult Common Bean Weevil {Br^^chus obtectus Say), greatly enlarged: 

 hair line at right shows real length. (From U. aS. D. A. Farm. Bull. 983.) 

 Fig. 122. — Work of Bean Weevils, natural size. (Original.) 



and lay their eggs for another generation which will develop in the same 

 seeds if these are kept where it is fairly warm (Fig. 122), 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 (Bruchus 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. 



The Broad Bean Weevil {Bruchus rufimanus Boh.) in its life and habits more 

 nearly resembles the Pea Weevil than the other species above considered. It is 

 injurious in Europe and Northern Africa and has now established itself in Cali- 

 fornia. The beetles resemble the Pea Weevil but seem to prefer broad beans or 

 horse beans. They appear in the fields in March and lay numbers of eggs on the 

 bean pods and the grubs on hatching make their way to the young beans, several 



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