136 CEREAL AND FORAGE INSECTS. 



Many attempts were made to determine the exact incubation 

 period of the egg. In most cases when a pea bearing an egg is 

 removed from the pod, decay and fungous growths cause its destruc- 

 tion before it can hatch. Some, however, were obtained which 

 remained in good condition long enough to hatch and in other cases 

 freshly laid eggs were removed and placed on damp blotting paper. 

 After repeated trials 3 eggs, whose age was accurately known, 

 hatched. One hatched in four days and the other two in six days 

 each. Enough other records were obtained under less accurate con- 

 ditions to show that the normal incubation period is five or six days, 

 with a shorter time when the temperature averages higher. 



THE LARVA. 



The brown mandibles of the larva show through the delicate mem- 

 branous covering of the egg before hatching. The shell is broken 

 by the abrasion of the mandibles, and by its contortions the larva 

 works the almost invisible shell backward off its body, whence it is 

 finally discarded as a minute white pellet. The larva lies extended 

 in the egg and after hatching appears sluggish, beginning to feed on 

 the tissue in its immediate vicinity and making no effort to change 

 its position. It gradually turns toward the inside of the pea, grow- 

 ing almost as fast as the pea is consumed. In nearly every case it 

 eventually gets into the central cavity, which is present between the 

 two halves of a growing pea. A semiliquid, pale yellow frass 

 appears and finally closes the comparatively small opening through 

 which the entrance to the pea was made. Unless it is too small to 

 afford sufficient food or too dry to be edible, a larva seldom leaves 

 the pea in which the egg was originally placed, until ready to pupate. 

 In one or two instances, where the pods in breeding cages were 

 allowed to become too dry, half-grown larvae were found wandering 

 along in the pod looking for suitable food. When placed in holes 

 cut in fresh peas they went at once to feeding and completed their 

 growth. 



During its growing period a larva consumes about one-third the 

 volume of a normal pea (fig. 68, d). Very rarely two larvae reach 

 maturity in one pea, but never more, although several eggs have 

 been found in close proximity. 



It is difficult to determine how many times a larva molts. The 

 exuvium is so ephemeral that no part of it can be found except the 

 cast of the head. Two of these brown head castings are often found 

 in one burrow, but the writer has been unable to find more. The 

 increase in size is gradual, without apparent change as to the char- 

 acters of the larva. 



Mr. W. D. Pierce states that "the species of the genus Chalcoder- 

 mus pupate in the feeding cells instead of entering the ground." 



