36 NINETEENTH REPORT STATE ENTOMOLOGIST OF MINNESOTA—1IQ22 
regions are comparatively high in protein, whereas the other parts 
of the tree contain little protein, but are high in carbohydrates. The 
differences in food value of the different parts of a log result in the 
definite localization of certain insects within the log. These differences 
also lead to variation in the rate of insect development, depending 
upon nutritional conditions. Thus we find the rapidly developing insects 
localized in the areas in which the wood is most nourishing, 1.e., the 
cambium and phloem. The insects in the heart wood develop, as < 
rule, quite slowly. In some cases development is made possible or 
the rate of development is hastened by the presence of microorganisms 
in the wood. These organisms, having the ability to convert cellulose 
into proteins, sugars, and starches, increase the nutritive value of the 
wood. It has been shown that many insects are unable to develop in 
the absence of these organisms. In logs, the process of decay depends 
largely upon the the character of infection and the time at which the 
organisms gain entrance into the log. Insect infection often determines 
to a very marked degree the time and the extent of fungous infection 
in the log. 
One of the factors which is obviously of the greatest importance 
in regulating insect activity within the log, is heat. Since a large pro- 
portion of the light which strikes upon the log is converted into heat 
units, it is very difficult, in the effect upon insects, to distinguish be- 
tween these two factors. Heat may be divided into optimum, active, 
dormant, and fatal zones, and theoretically light may also be thus 
divided. The effect of temperature has been shown to vary according 
to humidity conditions. There is evidence that variations of light 
intensity also influence the effect of temperature upon insects. It 
has been shown by experiments and observations with Chrysobothris 
adults that changes of temperature may bring about changes in the 
reaction of insects to light. Differences in temperature conditions as 
they occur in nature are sufficient to account for the great differences 
in the length of life cycles of insects which have been observed. This 
is well illustrated in Monochammus which may, under favorable con- 
ditions, complete its development in a single season, whereas under 
less favorable conditions two or even three years are required. 
The correlation of temperature, light, and relative humidity read- 
ings with the active periods of the insects living under natural con- 
ditions has shotvn that conditions favorable for the activity of one 
group are not necessarily favorable for the activity of another group. 
Monochammus adults appear to have an extremely wide range of 
active temperature, and for this reason fly at almost any time during 
