THE GENUS DENDROCTONUS. 39 



parts of the broods complete their development and emerge during 

 the first season, and the others remain over until the next season, it 

 will be a partial development of a seasonal generation. If all of the 

 broods develop and emerge within twelve months from the time the 

 first eggs were deposited, it is referred to as a complete annual 

 generation. 



Hibernation. — The term " hibernation " as here applied relates to 

 the period in the seasonal history of the broods from the time general 

 activity ceases in the fall until the time it begins again in the spring. 

 In southern localities there may be considerable activity (feeding 

 and development) of the broods during the warmer days of winter, 

 so that hibernation used in this connection does not mean that the 

 broods are entirely dormant and inactive, but that for the greater 

 part of the time they are. 



Overwintering stages. — The overwintering stages are those of the 

 hibernating broods. 



Overwintered broods. — The term " overwintered broods" relates to 

 all stages which have passed the winter in the bark of the infested 

 trees, whether active or not. It is, therefore, a better term to use 

 for the barkbeetles than " hibernated broods." 



Activity of overwintered broods. — By the " activity of overwintered 

 broods" is meant the feeding, development, transformation, emer- 

 gence, flight, etc., from the time general activity begins in the spring 

 among the broods which have overwintered in the bark. This 

 activity may extend over several months and overlap the activity 

 of broods of one or more generations. The parent adults that attack 

 the tree too late in the fall to complete their egg galleries usually con- 

 tinue their work of extending the galleries and depositing eggs when 

 activity begins the following spring. Some of the parent adults 

 that have completed their egg galleries in the fall may also live over 

 winter and excavate new galleries when activity begins in the spring. 

 The overwintered broods of young adults include those that trans- 

 formed to adults before activity ceased in the fall and passed the 

 winter in the pupal cells where they transformed. These are usu- 

 ally the first to emerge and fly in the spring, but sometimes they 

 remain in the bark until the majority of the broods are fully devel- 

 oped. Among the overwintered broods of larvae there may be all 

 stages from very young or small larvae to fully developed ones. The 

 latter will begin activity by transforming to pupae. The immature 

 larvae begin their activity by feeding and extending their larval mines. 

 Under normal or favorable conditions, the majority of the immature 

 stages of some species will have completed their development and 

 transformed to adults before the overwintered young adults in the 

 same tree have begun to emerge, so that nearly all of them may 

 leave the trees about the same time, but there are always certain trees 



