EFFECT OF PHYSICAL FACTORS IN ECOLOGY OF INSECTS IN LOGS 33 
Fatal Temperature of Insects in Logs 
A consideration of temperatures fatal to insects in logs is essential 
if we are fully to appreciate the significance of subcortical temperature. 
The fatal temperature varies with the species and also with the indi- 
viduals within the species. As a rule, however, a large proportion 
(about eighty per cent) of the individuals of a species will succumb at 
approximately the same temperature, and those dying above or below 
this point must be regarded as erratic. The presence of about twenty 
per cent of these erratic individuals makes it necessary to use a suffi- 
ciently large number of specimens in each set of experiments to make 
clear the distinction between normal and erratic. 
In these experiments Pityokteines sparsus Lec. served as a repre- 
sentative of the bark beetles and Chrysobothris dentipes as a representa- 
tive of the Buprestids. It must not be assumed, however, that the other 
species necessarily have the same fatal temperature as these, but it is 
reasonable to assume from the results of these experiments that Pityok- 
teines sparsus represents a group having a fairly low fatal temperature, 
whereas Chrysobothris represents a group having a high fatal tem- 
perature. 
The experiments with Pityokteines sparsus were conducted without 
removing the insects from the logs. The logs containing the insects 
were exposed to full sunlight and the temperatures within the logs 
were recorded every fifteen minutes. As the various degrees of tem- 
perature were attained some of the pieces were removed to a cool 
place and the condition of the insects was noted. These experiments 
show that 43°C. marks the upper limit of activity, and 47°C. the fatal 
temperature for this species. Between 43°C. and 47°C. the insects 
are in a state of estivation. The fatal temperature for adult speci- 
mens of Chrysobothris is about 52°C. No disturbance of the ability 
of these insects to control their movements was noticed until a tem- 
perature of 51°C. was attained. From this it appears that the zone 
of estivation is very narrow with Chrysobothris. That larvae of 
Chrysobothris are able to endure extremely high temperature is indi- 
cated by their occurrence on the upper side of logs lying in full sunlight. 
Cerambycid larvae are as a whole less able to endure high tem- 
peratures than Chrysobothris. They are seldom found developing 
normally on the upper side of logs exposed to full sunlight, but usually 
confine their activities to the sides and bottom of such logs. Under 
partial shade, however, they are active on the upper side. 
