20 ANNUAL REPORTS 01 DEPARTMENT OF AGRICULTURE, 1953 
Available Soil Moisture Close!) Associated \\ i t li Hark Beetle Attack 
Continuous studies have been under way for more than 1<> years in 
northern ( Jaliforaia to determine the relation of climate to damage by 
bark beetles. An analysis of records obtained indicates thai available 
soil moisture is the dominant climatic factor associated with bark 
beetle injury. During the LO-year period < Vx percent of the annual 
loss was correlated with temperature, precipitation, and the resulting 
soil moisture during the growing season. 
New Epidemic of Engelmann Spruce Beetle in Northern Rockies 
An epidemic outbreak of the Engelmann spruce beetle occurred 
early in the summer of 1952 in spruce forests throughout northern 
Idaho and northwestern Montana. This outbreak probably devel- 
oped in tremendous numbers of spruce uprooted by hurricanelike 
wind- in November 1940. The Colorado outbreak of this beetle, 
which developed in windthrown timber following a blowdown in 1939 
and eventually destroyed -1 billion feet of valuable timber, subsided in 
L952 following an extensive program of chemical control plus the 
destruction of Large numbers of the beetle by abnormally low winter 
temperatures and By woodpeckers. 
Simplified Eiigelmann Spruce Beetle Spray Fulfills Expectations 
Previous reports have called attention to the effectiveness of 
ethylene dibromide emulsions in controlling the Engelmann spruce 
beetle. [nasmuch as this formula utilizes water rather than oil. its 
development was considered to represent a progressive step in the 
search for more economical methods of control. The new emulsion 
formulation was tested in the field in 1952, being used in two control 
projects in Colorado, in cooperation with the Forest Service. Ap- 
proximately 40,000 gallons of this emulsifiable concent rate containing 
3 pounds of ethylene dibromide per gallon was prepared at Denver. 
Colo., for use ill these tests. The emulsion fulfilled all expectations, 
not only as an effective bark beetle insecticide but also a- a relatively 
pleasant and safe formulation for control personnel to apply. Tests 
were initiated on the usefulness of glycidyl phenyl ether and epi? 
chlorohydrin in preventing corrosion of tin plate containers by the 
formulation, which is packed in gallon cans for field use. 
Trap Frees May He Useful in Ku<j;eliiiann Spruce Beetle Control 
Studies begun in Colorado in L951 were continued in cooperation 
with the Forest Service to determine the possibility of obtaining con- 
trol of the Engelmann spruce beetle by the systematic felling of trees 
and their subsequent removal from the stand after beetle attack and 
prior to beet le emergence. 
Several thousand trees were felled and left in the woods until the 
end of the L952 beetle flight season, at which time they were exam- 
ined lor evidence of attach. Despite a light infestation of spruce 
beetle- in L952, it was found that even where practically all telled 
tict- were infested, only -J percent of the standing green trees were 
infested. These results, while not demonstrating the value of this 
