38 NINETEENTH REPORT STATE ENTOMOLOGIST OF MINNESOTA—19Q22 
It was found that some insects are very exacting in their requirements 
and occur only in narrowly limited areas. For example, Hylurgops 
pinifex is always found in cool moist locations. Unfortunately, the 
attempt to measure the moisture content of logs was not attended with 
much success because of the few observations which could be made 
during the season. For this reason a direct experimental correlation 
of this factor with insect activity was impossible. 
The effect of the physical factors of the environment upon insects 
in logs is well illustrated by the distribution of these insects under 
different conditions. The effect of high temperature is clearly shown 
in logs in the open. On the upper side of these logs are found only 
insects which are most resistant to heat, such as Chrysobothris. In 
the cooler portions, however, other species make their appearance. 
Under the shade where cooler conditions obtain, the heat loving insects 
disappear, whereas the insects which develop best under cool condi- 
tions become more and more abundant with increasing shade. Three 
quarters shade was the heaviest used in these experiments. Under 
this condition no Chrysobothris was present and there appeared to 
be some indications of a reduction in abundance of Monochammus. 
Under these conditions there was a distinct reduction in the develop- 
menial rate of all species represented. From this it seems probable 
that still greater shading would check Monochammus as well as Chrys- 
obothris. If this is true, the shading of logs which must be left in 
the woods over the summer season by covering them with brush or in 
some other way, may prove the most satisfactory method for control- 
ling wood-boring insects. 
From this series of experiments no attempt has been made to 
formulate definite recommendations for controlling wood-boring insects. 
Rather than to present a solution of an immediate problem the aim 
of this work is to lay a foundation for further investigations of a 
more .immediate practical nature. These experiments, however, have 
shown conclusively that the activities of wood-boring insects are con- 
trolled very decidedly by the action of external factors, and that the 
zone of their optimum development is often very narrow. These 
results indicate that further investigations may make possible the 
formulation of simple, inexpensive, and practical control measures. It 
will, in all probability, be possible to control wood borers by very 
slightly modifying the present-day methods of handling logs. If this 
work can form the basis for further development in the control of 
injurious wood borers, it will have justified the expenditure of all the 
time and energy required in its prosecution. 
