June, ’24] 
graham: temperature and subcortical insects 
379 
average. It would appear that if it were not for these erratic individuals, 
adaptation of a species to new or changed environmental conditions 
would be difficult if not impossible. 
Subcortical Temperature Conditions 
Most of us think of bark as an excellent insulating material, and from 
this idea the assumption arises that a log may be regarded as a buffer 
medium and that the forms of life beneath the bark are protected to a 
large degree from sudden temperature changes and from extremes of 
temperature. The insulating power of bark is not so great as we usually 
suppose. The work of Craighead (1920) calls the attention of ento¬ 
mologists to the high temperatures that occur under the bark of logs 
lying in the sun. He points out that solar radiation may raise the sub¬ 
cortical temperature above a point fatal to the insect inhabitants of the 
logs. The author (1920) has shown that the chief factors influencing 
subcortical temperatures may be summarized as follows: 
1. Solar radiation 
a. Light intensity 
b. Solar altitude 
c. Angle of incidence 
2. Character of bark 
a. Color 
b. Surface 
c. Structure 
d. Thickness 
3. Air temperature 
4. Air movement 
5. Evaporation from bark surface 
6. Proximity to other radiating or absorbing surfaces 
The highest temperatures recorded in these experiments were ob¬ 
served beneath the dark colored bark of white pine: Color of the bark 
determines to a very considerable degree the amount of solar heat ab¬ 
sorbed by the bark surface. Thus, other things being equal, the darker 
the bark the higher the subcortical temperature. Frequently the noon 
temperature exceeded a point fatal to most insects and several times 
exceeded 60° C. Table II, shows the subcortical temperatures that 
were observed at noon under various shade conditions. The influence 
of character and thickness of the bark is illustrated in Table III. 
