466 
JOURNAL OF ECONOMIC ENTOMOLOGY 
when the surface of the sapwood is reached is continued longitudinally 
upward as the egg-gallery. After being fertilized the female beetle 
continues extending the egg-gallery. At each side she gouges out small 
niches, in each of which a single egg is deposited. In this process the 
beetle extends the gallery with her mouth parts. When it has been 
carried slightly beyond the last egg-niche she constructs another niche. 
Then in order to deposit the egg it is necessary that she back out of the 
burrow to the surface of the bark, reverse herself and re-enter the burrow 
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Fig. 11.—Graphs showing excess and deficiency in precipitation at Syracuse from 
1908-1922 and relation to injury by the hickory bark-beetle. The rather close para- 
lelling of the graph showing annual precipitation and that showing the conditions 
for the'three growing months (June, July and August) is interesting in demonstrating 
that most of the departure from normal came during these three months. Also note 
that the incidence of the epidemic came on the year when the deficiency in precipita¬ 
tion for the growing months became greater than for the entire year. Note also that 
from this point on the graph representing the departures during the Summer months 
remains well below that representing the departures for the year—i. e. the deficiency 
is always greater and the excess always smaller, there being an excess only in 1915 and 
1922. The effect of the excess in 1922 was slight as it was due to two very heavy 
rains occurring rather early in June. The graph showing “Trees Killed” is based on 
actual counts from 1912-1918. After that the number killed is estimated, due to the 
wide spreading of the epidemic from its place of incidence. 
