12 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
Infestations of the beech scale and fir-bark louse in the Northeast 
are periodically reduced to a minimum when an abnormally cold winter 
occurs. In regions where the mimimum temperatures are —10°, or 
lower, the European pine-shoot moth need not be feared in pine planta- 
tions. The southern pine beetle is killed at temperatures of from 10° 
to —15°, depending upon the stages concerned; thus, extremely cold 
winters prove fatal to a high percentage of the broods of these bark 
beetles and definitely limit the nor thward extension of their range. 
Severe late frosts or freezes, occurring after the new growth of the 
trees has begun in the spring, fr equently completely check outbreaks 
of defoliators dependent on tender foliage for development in the early 
instars. But late frost also causes much damage to the tree, preparing 
it for borer attack as described under Defoliation (pp. 15-16). 
Altitude and exposure, by modifying temperature, regulate insect 
activity, determine the number of insect generations per year, and con- 
trol the distribution of insect species. This has been fully discussed 
by Miller (303), Chamberlin,’ and Beal (26). 
MOISTURE 
Moisture has an important bearing on insect abundance, both through 
its direct effect on the insects and indir ectly through its influence on 
the hosts. Some insects require very moist conditions i in order to work 
to the best advantage and are killed by dryness; others require very 
dry conditions and are killed by moisture. Moreover, moisture, 
through precipitation, has an important influence on the growth of 
trees and their resistance to bark beetle attack; and flooding or exces- 
sive soil moisture may weaken the trees. 
DROUGHT 
Several recent droughts in the East have given clear-cut evidence 
of the importance of this factor on subsequent insect outbreaks. Dur- 
ing the summer of 1924, in eastern Texas and western Louisiana, and 
more locally in Mississippi, there was a deficiency in rainfall for sev- 
eral months, resulting in the severest drought on record for these 
areas. Pine trees infested by bark beetles (Ip ps spp.) began dying late 
in the fall and continued to die through the winter, resulting i in the 
death of over 100 million board feet of mature longleaf pine. 
From October 1931 to May 1932 northern Flor ida and southeastern 
Georgia experienced a similar drought, resulting in the death of many 
million board feet of timber, largely second- ‘orowth stands. Both 
round and turpentined stands were affected. [ps beetles attacked 
much of this timber, and there was considerable agitation by lumber- 
men and timber owners for undertaking w idespread control opera- 
tions. At that time the Bureau of Entomology of the United States 
Department of Agriculture pointed out, however, the secondary char- 
acter of the attack and recommended against such measures. With 
the return of rains, all trouble subsided. 
Throughout the Northeastern States there was a marked drought in 
1930, so severe in some places that hardwood trees lost their foliage 
during the summer. The following year hemlocks began to die in many 
sections, and the losses continued to increase for several years. In 
*See footnote 4, p. 4. 
