34 NINETEENTH REPORT STATE ENTOMOLOGIST OF MINNESOTA—I9Q22 
The Influence of Moisture upon Insect Activity Within the Log 
The effect of moisture upon insect activity has been shown to be 
important. Shelford, Pierce, and others have shown that the optimum 
temperature and the limits of effective temperature are greatly influ- 
enced by humidity. By analogy it is reasonable to suppose that this 
factor, the importance of which has been demonstrated for other in- 
sects, is also of great importance to insects working in logs. The work 
of Henning (1907) demonstrates that Ips typographus is influenced 
in every stage of its development by this factor. 
The influence of the relative humidity of the air is probably not of 
such great importance to insects living within the log as 1s the moisture 
content of the wood and inner bark. It does, however, have an influ- 
ence upon rate of evaporation and therefore upon the rate of drying 
of the log. 
Distribution of Insects Under Different Conditions 
An examination of the distribution of the different insects under 
the four environmental conditions studied shows that these insects may 
be grouped according to their ecological requirements. Under one set 
of conditions certain species develop at the optimum rate. Under other 
conditions development is slow, and under still others it is impossible. 
Unfortunately the habits of different groups of insects are so variable 
that it seems almost hopeless to find any method of handling and 
storing logs that will prevent all insect infestation. Nevertheless when 
we remember that not all insects working in a log are injurious, as 
some do not enter the wood, we realize that our problem is not quite 
so difficult as it first appears. When we can check the development 
of the true wood-boring forms, our chief aim has been attained. 
The study of the distribution of insects under different environ- 
mental conditions illustrates how the species are grouped according to 
their ecological requirements. The results may be outlined as follows: 
Group 1. Insects requiring high temperatures for development— 
represented by Chrysobothris. 
Group II. Insects unable to endure extremes of temperature or 
moisture—represented by bark beetles such as [ps pini. and by Mono- 
chammus. 
Group III. Insects requiring cool moist conditions—represented 
by Hylurgops and some Cerambycidae. 
The insects of Group I are found on the upper side of logs in 
full sun, one-third shade, and to a lesser extent in one-half shade. 
They are usually most abundant in full sun altho this varies with the 
