April, '11] SCHOENE: CABBAGE MAGGOT 213 



Larval Stages and Number of Days Required for the Larva to Mature 



Efforts to breed the insect in the laboratory and to observe the 

 larval ecdyses have not met with success. Some cast-skins were 

 secured, but not with sufficient regularity as to be certain of the stages. 

 Tlje data given below in Table III was secured by growing in the 

 laboratory a number of larvse which were hatched the same day. 

 Each succeeding day several of these were killed and preserved. By 

 this means a series of larvse were obtained which ranged in age from 

 one to eighteen days. One or more larvse of each lot was measured 

 and the cephalo-pharyngeal skeleton mounted in balsam. A study 

 of the chitinous structures indicate three well-marked stages for the 



Fig. .5. Relative sizes of cephalo-pharyngeal structures of 1st, 2d and 3d 

 stages of larva of Pegomya brassicoe. Camera lucida drawings x 65. (Original.) 



larvse. These instars may be known by the difference in the size and 

 shape of the cephalo-pharyngeal structures. The increase in size of 

 the different individuals of the series was not proportional to the age. 

 In some instances larvae of the same age would vary so in size that 

 one would be three times as large as the others. These variations 

 did not appear in the chitinous structures of these individuals. Aside 

 from the differences in size which mark the three stages, there is a 

 thickening or blackening of the chitin which becomes very pronounced 

 in the older larvse. Thus the amount of pigment, together with the 

 size of the skeletal parts would indicate the age of the larvse more 

 closely than the dimensions of the individual. 



In the examination of the larvae previous to the separation of the 

 chitinous structures, it was noted that all the larvse possessed the 

 bifed caudal tubercles ascribed to brassica by Fitch in his eleventh 

 report. 



