406 WEST VIRGINIA EXPERIMENT STATION 



curely protected by a thin wall of cemented borings between it 

 and the main gallery, If the conditions of the bark are favor- 

 able when the larva emerges from the egg, it commences to 

 feed, and extend a short, gradually widening mine at right 

 angles to the brood galleries and just above, or barely through 

 the inner layer of bark for a distance of about one-fourth of an 

 inch, or three to four millimetres, when it cuts through the in- 

 ner layer and gnaws out an irregular cavity two to eight mil- 

 limetres wide and eight to ten millimetres, long, Fig. LXViI,in 

 which it undergoes the greater part of its development. 



When nearly matured, it bores through the outer layers of 

 the inner bark, and as soon as it is fully developed it enters 

 the outer corky bark and excavates, an oblong pupa case, Fig. 

 LXiX, in which it changes to the pupa, and finally to the 

 adult. When the adult is fully developed, it bores directly out 

 through the bark, leaving a clear cut and exposed hole in the 

 surface. Should the conditions of the bark from any cause, be 

 distasteful to the young larvae, or not in proper condition for 

 its nourishment, which is often the case, it continues to bore 

 for a long distance through the inner layer or through the in- 

 ner portion of the bark, without increasing in size, as is indi- 

 cated by the uniform width of the mines as show in Fig. LXV1II. 



HABIT OF FLIGHT. 



From such observations as I was able to make with reference 

 to the flight of this insect,and finding examples in electric light 

 globes, it would appear that it flies at night as well as during 

 the day. It would also appear from the character of the attack, 

 that at certain times during the invasion, probably from July to 

 September, and possibly in May, great migrating swarms oc- 

 curred which ascended high in the air and were evidently car- 

 ried long distances by strong winds and storms. 1 This is indi- 

 cated by the fact that the first groups of trees that died from 

 its attack in a newly invaded locality, were usually on high 

 exposed points and mountain slopes, where the swarms would 



1. The wings which are exceedingly long as compared with the size of the insect, are 

 particularly favorable for the action of the wind in carrying them'long distances. 



