EFFECT OF PHYSICAL FACTORS IN ECOLOGY OF INSECTS IN: LOGS 29 
Both these factors are exceedingly important in their influence. 
upon insect activities. Insects vary both within the species and between 
species as to their reactions to these factors, but in each case tempera- 
ture and probably light also can be divided into optimum, effective, 
high and low dormant, and high and low fatal zones. It seems prob- 
able, however, that light under natural conditions seldom goes beyond 
the limits of toleration for most insects. It does, however, have a 
stimulating effect as shown by Hennings (1907) who noted that Ips 
typographus Linn failed to develop normally in the absence of light, 
and by the fact that Chrysobothris adults remain inactive on cloudy 
days at temperatures equal to or higher than the temperature at which 
they are active on sunny days. 
The influence of heat and of light converted into heat may be 
observed in all stages of insects -from egg to adult. Hennings (1908) 
has shown the effect of different degrees of temperature and humidity 
upon each step in the life history of [ps typographus Linn. Some of 
his results are set forth in Table II. 
In correlating the period of activity of Chrysobothris adults, our 
experiments show that of the factors which influence the activity of 
these insects, temperature ranks first and light next, while relative 
humidity appears to have little influence. Under bright conditions 
activity begins at 26°C. and full activity is reathed.:at 30°C. Under 
cloudy conditions they remain inactive until 29°C. With these insects 
there seems to be a marked daily periodicity which appears to be inde- 
pendent of both light and temperature. Regardless of conditions they 
are seldom active before 8:30 a.m. or after 4:30 p.m. 
Some other Buprestids appear to have a somewhat lower active 
temperature, since Chalcophora and Dicerca were observed flying when 
conditions were not favorable for Chrysobothris. In contrast to the 
narrow range of activity of Chrysobothris, Monochammus was observed 
actively feeding and flying from early morning to sunset. 
~ The rate of larval development of wood-boring insects varies 
greatly, owing not only to quality of food, but also to temperature dif- 
ference. Monochammus will frequently come to maturity in a single 
season under favorable conditions, whereas under cool, shady conditions 
three years or even longer are required to complete development. 
Factors Influencing Subcortical Temperature 
The recent work of Craighead (1920) calls attention of ento- 
mologists to the high temperatures which occur under the bark of logs 
lying in the sun. That this is not the first time this phenomenon has 
been noted is evidenced by the repeated reference in bark-beetle 
