EFFECT CF PHYSICAL FACTORS IN ECOLOGY OF INSECTS IN LOGS 37 
the day. Chrysobothris, however, requires high temperature and bright 
sunlight before it reaches its maximum state of activity. Other bupres- 
tids, such as Dicera and Chalcophora, are active at lower temperatures 
than Chrysobothris. 
Subcortical temperature was found to be very variable in the same 
log. Also there was considerable difference between logs of the same 
species and still more between logs of different species. The subcortical 
temperature on the upper side of certain logs exposed to full sunlight 
often reached a temperature far above that fatal to insects. Craighead 
also found this to be true, and recommended that advantage be taken 
of solar radiation in the control of wood-boring insects. The present 
series of experiments has shown, however, that the application of this 
method is limited in its scope, and can not be applied to all logs under 
all conditions. Many heat resistant insects, such as Chrysobothris larvae, 
are able to withstand extremely high temperatures for short periods 
of time, and are thus able to survive and develop normally on the 
upper side of many logs lying in the sun. It is true that most insects 
succumb to such conditions. On the other hand, some logs, such as 
those of Norway pine, which have scaly bark, highly efficient as an 
insulator, never reach extremely high temperatures. 
Solar radiation, the character of the bark, air temperature, air 
movement, evaporation from the bark surfaces, and proximity to other 
radiating or absorbing surfaces, are the most important factors control- 
ling the subcortical temperature of logs. 
The fatal temperature of insects, like their effective temperature, 
varies under different conditions. There is considerable variation 
within a single species and even greater differences between different 
species. From the series of experiments described in this paper it 
appears that Chrysobothris has a much higher fatal temperature than“ 
any other of the insects studied. The adults were able to endure tem- 
peratures up to 52°C., while the larvae apparently were still more re- 
sistant to heat. Cerambycid larvae have a much lower fatal tempera- 
ture than Chrysobothris. The only bark beetle for which the fatal 
temperature was determined was Pityokteines sparsus Lec. It was 
shown to be comparatively low for this species of beetle, as they passed 
into, a state of estivation at about 43°C. and were practically all killed 
by a temperature of 47°C. This is about the point at which the majority 
of insects succumb. 
That moisture conditions within the log have an important effect 
upon the activities of xylophagous insects can not be doubted. This 
is shown by the distribution of beetles in logs under different conditions. 
