752 Journal of Agricultural Research voi.xx.No.io 



certain that in these experiments the maximum number of eggs was not 

 obtained. Available data indicate that approximately two-thirds of 

 all the eggs laid produce larvse. 



As a result of there being two periods of adult emergence there are two 

 periods of oviposition and incubation during the year, coincident with 

 those of issuance, the first occurring in the late spring and early summer 

 (particularly May and June) and the second in the late summer and early 

 fall (late July, August, and early September). 



The period of incubation as determined by the time elapsing between 

 the laying of the first egg and the hatching of the first larva varies from 

 13 to 21 days with an average, from six experiments, of 16 days. 



For the first 5 or 6 days after oviposition very little change is noted 

 in the eggs, but beginning with the seventh or eighth -day a gradual 

 swelling is evident, so that by the ninth day there is a slight separation 

 of the sides of the mouth of the egg pocket. This separation increases 

 until it is 0.5 mm. in breadth shortly before the egg hatches and the larva 

 emerges. 



The length of the larval feeding period, from the hatching of the eggs 

 to the appearance of the first prepupa, varies from 25 to 31 days, with 

 an average of 28 days. 



During the whole of the feeding period the larvae are gregarious and 

 show little or no tendency to disperse. If disturbed while feeding they 

 throw back the head and thorax and remain motionless in that attitude, 

 attached to the needle only by the uropods. 



The larvse for the first, second, and third stages eat only the epidermis 

 and the immediately adjoining tissue of the needles. The approximate 

 length of the first stage is 6 days, of the second 5 days, and of the third 5 

 days. Beginning with the fourth stage and continuing through the 

 sixth, the larvse eat the whole of the needle and occasionally portions of 

 the tender bark on the young twigs (PI. 92 , A) . Field observations on the 

 feeding upon the bark seem to indicate, however, that the species of the 

 tree may have more influence than the amount of foliage available. The 

 bark of the jack pine (Pinus banksiana) in Wisconsin and Virginia was 

 usually fed upon, even though there was plenty of foliage available. 

 The approximate length of the fourth stage is 5 days, of the fifth 4 days, 

 and of the sixth 4 days. 



Following the larval feeding period comes the prepupal instar, a larval, 

 nonfeeding, cocoon-spinning, quiescent stage. The prepupae first seek a 

 suitable place and then spin their cocoons. In nature the cocoons have 

 only been found several inches under the surface of the ground under the 

 tree attacked. 



After the cocoon is made the insect remains for a comparatively long 

 time as a prepupa, but shortly prior to the time of its emergence it trans- 

 forms to the pupa and then develops rapidly into the adult stage, which 



