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graham: temperature and subcortical insects 
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TEMPERATURE AS A LIMITING FACTOR IN THE LIFE 
OF SUBCORTICAL INSECTS 
By Samuel A. Graham, Division of Entomology, University of Minnesota 
Abstract 
The distribution of insect species within a log depends to a very large degree 
upon the temperature in different parts of the log. The most heat resistant groups, 
of which the genus Chrysobothris is representative, are found only in the warmer 
parts, whereas those species less resistant to heat are found only where extremely 
high temperatures do not occur. On the basis of temperature it is possible to divide 
the insect inhabitants of a log into several ecological groups. 
The importance of temperature as a limiting factor in the life and 
distribution of insects in general has long been recognized by biologists. 
In most of our discussions of the effect of temperature upon the dis¬ 
tribution of terrestrial organisms we have thought most frequently in 
terms of large areas, but now we are beginning to realize the importance 
of this factor in limited environments. We now know that steep tem¬ 
perature gradients occur in very short periods of time or within very 
short distances. This explains many of the puzzling instances of perio¬ 
dicity and peculiarities of local distribution among certain insects. 
The effect of temperature upon the distribution of insects in a small 
