PEA AND BEAN INSECTS 59 



The young larva crawls actively about until it finds a bean which 

 it enters through a small round hole about y^ inch in diameter. 

 In about three days after hatching, the larva molts and assumes 

 the general appearance of the mature grub. The legs, eyes 

 and the long hairs on the abdomen are lost, the body becomes 

 proportionately shorter and thicker and the grub assumes a 

 curved position. The larva burrows diagonally into the bean 

 a short distance and there eats out a large cell covered in part 

 only by the thin semi-transparent outer coat of the bean. It 

 then lines the cell with a yellowish white paste, thus excluding 

 all excrement from the pupal chamber. The length of the 

 larval stage varies greatly with the 

 temperature, or from eleven to forty- 

 two days. The full-grown larva is ^ 

 to Y inch in length. The insect trans- 

 forms to a white pupa within the cell 

 and remains in this stage from five to 

 eighteen days. Soon after transforma- 

 tion, the beetle neatlv cuts out a Fig. 43. — Beans showing 



circular lid through the seed-coat of Zl^!'' "'^^' ^'^ '^^ 

 the bean and makes its escape (Fig. 



43). The entire life cycle requires from twenty-one to eighty 

 days. The beetles emerging in the field soon begin laying eggs 

 for another generation. The number of generations that occur 

 in the field depends on the temperature and the length of the 

 season. Breeding is continuous in stored beans provided the 

 temperature is sufficiently high. In the vicinity of Washing- 

 ton, D. C, there are probably six generations annually. The 

 number of weevils reared from a single bean depends on the 

 size of the seed. In cases in which the beetles are allowed to 

 breed in stored seed undisturbed, they often reduce the contents 

 to a powdery mass held together by the hull. As many as 

 twenty-eight weevils have been reared from a single bean. 

 Weevily beans are unfit for planting. In a large proportion of 



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