August, ’24] 
BLACKMAN: HICKORY BARK BEETLE 
465 
be little doubt that the continued deficiency results in a considerable but 
variable reduction in the vitality of the tree and increases (either much 
or little depending upon the individual tree) its susceptability to destruc¬ 
tion by the bark-beetles. On May 7, 1924, increments were taken of ten 
living hickory trees growing under more healthy conditions in a woodlot 
about 2 miles south of the original center of infestation. Here there was 
no evidence of present or past activity of the hickory bark-beetle. The 
increments showed considerable individual variation but the average 
condition as compiled from the ten trees is as follows:—a gradual de¬ 
crease in the increment from 2.2 mm. in 1907 to 1.5 mm. in 1914; an 
increase to 1.7 mm. in 1915; and again a decrease to 1.1 mm. in 1923. 
In the view of the writer, after considering all of the data given and 
other data appearing later, the weakened condition of the tree is not 
sufficient fully to account for the rapid increase in the number of the 
insects and the resulting increase in the trees killed. It would seem, 
however, that an abnormality in precipitation during the months of 
June, July and August would have a decided direct effect upon the in¬ 
sects themselves—either favorably or adversely. It is believed that this 
direct effect would be of more importance in fostering an epidemic and 
certainly of greater importance in checking one than would be the in¬ 
direct effect upon insects as exerted through its influence on the health of 
the tree. That any deficiency cr any excess in rainfall during the three 
months period or any excess of cloudiness during the latter part of it 
would have an effect upon the beetles or their younger stages can be 
understood better when we consider the habits and seasonal history of 
the bark-beetle. 
The hickory bark-beetle passes the winter as a fully grown larva in 
the outer portion of the inner bark of its host tree. The adult beetles 
emerge at Syracuse during the latter part of June, throughout the month 
of July and during early August. The height of emergence usually 
occurs during the first two weeks in July, but varies somewhat accord¬ 
ing to the advancement of the season. The adults fly at once to living 
hickory trees and feed for some time by boring into the young twigs 
and into the bases of the leaf-petioles. After feeding for some time— 
exactly how long is not known—the beetles fly to the trunk and branches 
where they may often be seen in hundreds creeping over the bark and 
examining every crack and crevice. Each female selects some place 
where the bark is thin, as in one of the longitudinal cracks, or under one 
of the loosened scales, and begins to construct her burrow. The en¬ 
trance tunnel extends through the bark at a slightly upward angle and 
