INSECT ENEMIES OF WESTERN FORESTS 193 
They are completely limbed and the brush cleared away so that the 
logs will receive direct sunlight. After a few day’s exposure with 
air temperatures of 80° F. or more all of the bark beetles on the 
top half of the logs will have been killed. Then the men return and 
with peavies turn the logs completely over so that the other side 
will be exposed. 
This method has been very effectively used for several years in 
control of the mountain pine beetle in Crater Lake National Park. 
It has the advantage of being much cheaper than either the peeling 
or burning methods; and in crowded stands it avoids the scorching 
of adjacent trees, and thus does not set up influences attractive to the 
beetles which would favor reinfestation, as so often happens when. 
the logs are burned. The disadvantages are that considerable slash 
is left in the woods, and the method cannot be used in the shade 
of dense stands, on cold north slopes, or in localities where air tem- 
peratures during the control season are less than 80° F. 
Submerging the infested logs 
Many years ago A. D. Hopkins advocated the submerging of in- 
fested logs as a means of destroying bark beetles where the infested 
trees could be cut and placed in a mill pond. Recent experiments 
have shown that infested logs must be submerged for at least 6 
weeks in order to destroy the broods of the western pine beetle. In 
any shorter period than this the beetle’s development is simply 
retarded. Also, the beetles in the portion of the logs not covered by 
water are unhampered in their development and are free to emerge 
and escape. So far this method has been tried only in an experi- 
mental way, but it has possibilities, where applicable, and some- 
time may be of value in connection with a control project. 
The trap-tree method 
A method of bark-beetle control that has been used in Europe 
with apparent success consists in felling injured, weakened, or sup- 
pressed, noncommercial trees in accessible locations as attractive 
baits for bark-beetle broods, and then destroying them after the 
beetles have entered the bark. The method has been tried on numer- 
ous projects and on rather an extensive scale in California and 
southern Oregon in the control of the western pine beetle, but with 
little success. Although beetles are attracted to the traps, these 
fail to protect the standing trees in the vicinity, and frequently 
the trap tree acts as a source of attraction to bring in bark beetles) 
that kill groups of adjacent standing trees. Moreover, the trap 
trees have always failed to absorb any large proportion of the beetles 
in their area, and hence the method has lost favor as an effective or 
economical control measure. It may, however, prove of value in the 
control of other species, particularly in cases where the trap logs 
can be removed and utilized. 
Bark-beetle control by logging 
Where the infestations are in accessible tracts of valuable timber, 
the cutting and salvage of the infested trees through logging opera- 
tions is an effective and economical method of control. This method 
136650° —38——_13 
