BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 21 
method of control, do suggest the possibility of preventing epidemics 
by capturing and destroying a major part of the beetles present in 
light infestations. 
Two Nematodes Found Parasitizing Engelmann Spruce Beetle 
Recent studies of the effect of biological control factors on Engel- 
mann spruce beetle infestations in Colorado show that two species of 
nematodes, Aphelenchulus reversus and Parasitylenchus (new spe- 
cies), parasitized approximately 20 percent of the beetles in 1952. 
Laboratory studies showed that egg production by infested female 
bark beetles was reduced as much as 90 percent. These limited studies 
indicate that these nematodes may be of real importance in limiting 
bark beetle populations. 
Pacific Northwest Has Its Worst Epidemic of Douglas-Fir Beetle 
What has been characterized as the worst epidemic of the Douglas- 
fir beetle ever recorded in the Pacific Coast States occurred in 1951. 
The epidemic originated in the hundreds of thousands of Douglas-fir 
that were blown down in the Pacific Northwest during severe wind- 
storms in 1949 and 1950. In 1951 more than a billion board-feet of 
valuable timber was beetle killed. During the winter of 1951-52 a 
second windstorm occurred, adding still further to the huge volume of 
beetle-breeding material in the region. Indications are that the epi- 
demic will continue for several years. 
To determine the feasibility of aerial mapping and counting of trees 
killed by this beetle, Bureau personnel cooperated during 1953 with a 
timber company, the Oregon State Board of Forestry, and the United 
States Forest Service in an aerial survey. The results showed that, 
following a short period of training, qualified men could accurately 
map and make direct counts of beetle-killed trees over large areas from 
the air. To apply this technique it was necessary that the observation 
plane have good forward and lateral visibility and a slow-cruising 
speed of 60 to 70 miles per hour. Topographic maps or small-scale 
aerial photographs of at least 1-inch-per-mile scale are required for 
the area to be flown. The height of flight should be kept to a minimum 
of about 800 feet above the treetops. A ground check of each ob- 
server's work must be made to establish an air-ground correction factor 
for the counts of beetle-killed trees. 
Bark Beetle Ground-Survey Methods Improved 
Ground crews surveying Black Hills beetle infestations in the cen- 
tral Rocky Mountains have found no significant difference in effective- 
ness of the survey when stands are cruised in strips y 2 or 1 chain wide 
or when lines of plots of 0.1, 0.2, or 0.25 acre are tallied. The %-chain 
strip and the 0.1-acre plot can be surveyed faster than any of the 
others, provided the same length of line is used. In a direct compari- 
son of the ^-chain strip and the 0.1-acre methods, it was found that 
the former is faster, although not significantly so. Since it is easier to 
train personnel to do the strip rather than the plot survey, the former 
method will be used in future surveys. 
