BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 23 
insect broods beneath. These tests were so successful that during 
June 1939 an experimental control project was conducted on the 
Grand Teton National Park in Wyoming. 
BLACK HILLS BEETLE 
The Black Hills beetle is the most destructive forest insect in the 
central Rocky Mountain region. Since 1935 it has caused widespread 
losses in lodgepole, limber, and ponderosa pines, and in many areas 
has already destroyed more than 80 percent of the trees over 6 inches 
in diameter at breast height and all trees over 18 inches in diameter. 
The volume of losses caused by this insect during the past 5 years is 
seven times as great as the total fire losses and nearly as great as 
the total volume of timber cut in Wyoming, Utah, and Colorado. 
The timber cut during this period in 'these three States was about 
465 million board feet. 
The treating of over 50,000 ponderosa pine trees for control of the 
Black Hills beetle in the central Rocky Mountain region during the 
year brings the total for the last 5 years up to nearly a quarter of a 
million trees. The bark beetles built up to epidemic conditions during 
a period of severe drought and correspondingly poor tree growth. 
These outbreaks have been fought vigorously and effectively to save 
the scenic and commercial stands of pine in the region from further 
devastation. The actual treating was done by the Forest Service, 
the National Park Service, and the Denver Mountain Parks Improve- 
ment and Protective Association under the technical supervision of 
this Bureau. At present it appears that in practically all the areas 
where control work has been conducted the heavy epidemic centers 
have been reduced to an endemic condition. However, there should 
be no let-down in the vigilant watch for possible new centers of 
infestation. 
OTHER FOREST INSECT PROBLEMS 
HEMLOCK BORER 
A preliminary investigation in 1937 disclosed that about 100 million 
board feet of hemlock had died in stands on the Menominee Indian 
Reservation in central "Wisconsin since 1930. At the same time it 
was apparent that most of the trees had been infested by the hemlock 
borer. In June 1938 a study was begun to determine whether the 
insect is primary or secondary and whether any control measures are 
practical. From the first season's observations it can be definitely 
stated that the hemlock borer is secondary, since it can successfully 
attack and reach maturity in only those trees that are weak or dying. 
Incipient borer galleries in wood laid on as early as 1902 indicate 
that this insect has been present in these stands for many years. It 
could not, however, develop an epidemic population until severe heat 
and drought conditions from 1931 to 1937 and several severe blow- 
downs had made conditions favorable for successful attack and a 
rapid increase in population. General observations in the spring of 
1939 indicate less mortality of trees this year than last, due, it is 
believed, to the abundant rainfall and favorable growing conditions 
in 1938. However, more than one rainy season will be needed to alter 
noticeably the condition created by the prolonged period of dry years. 
