460 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 17 
common Australian pest pears. Of the nine remaining species available, 
six species have increased in a satisfactory manner. 
It is obvious, in view of the above facts and figures, that almost the 
entire present Australian effort relating to biological control of the 
prickly-pear pest is based upon the field and laboratory work in the 
United States. Considering the territory covered and the results 
achieved in forty months at an annual cost of three-tenths of the yearly 
appropriation, the whole operation in North America assumes an aspect 
of strict economy. 
The North American work is planned to cease in May or June, 1924. 
Provision should immediately be made to enable the Board to secure 
from Mexico and South America other valuable cactus destroyers. 
By such action several other natural enemies of pear would be rendered 
available to strengthen the reduced complex already introduced from 
North America. 
THE EFFECT OF DEFICIENCY AND EXCESS IN RAINFALL UPON 
THE HICKORY BARK BEETLE 
(.Eccoptogaster quadrispinosus Say) 
By M. W. Blackman, New York State College of Forestry, Syracuse, N. Y. 
Abstract 
An epidemic of the Hickory Bark-Beetle started in Syracuse in 1912 and has ex¬ 
tended to the present time, with a decided checking in 1915. This was preceded by 
semi-drought conditions over a period of several years before the epidemic started. 
While the trees were undoubtedly affected, as is shown by a study of the rings of 
growth, the indirect effect through the lessening of the vitality of the trees is not 
sufficient to account for all the phenomena. The greatest effect was the more direct 
one upon the insects themselves, as the deficiency came during the summer months. 
A deficiency at this time is beneficial to both adults and larvae, and an excess, as in 
1915, acts as a distinct check. When the adults are active, continued rain kills many 
while feeding and establishing their burrows and also checks egg-laying. Excess 
rainfall, humidity and cloudiness kills the larvae because it produces an excess of 
water in the plant tissues and this is set free into the larval mines. Deficiency in 
rainfall has a beneficial effect upon both adults and larvae. This may be put to prac¬ 
tical use. If it is known that there has been a deficiency in rainfall extending over 
several years, an intelligent lookout can be made for the first signs of undue increase 
of dangerous forms and these can be controlled before they reach epidemic proportions. 
For many years there has been a general feeling among forest ento¬ 
mologists that there is a more or less direct relation between drought 
conditions and the incidence of epidemics of insects—especially of boring 
insects. As a usual thing this feeling has been suggested or hinted at as 
