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FOREST INSECTS 

Effect of a mountain pine beetle infestation on a lodgepole 
pine stand.--A. L. Gibson, of the Goeur d'Alene, Idaho, field labo- 
ratory, reports as follows: The Beaverhead National Forest has 
been the scene of a severe outbreak of the mountain pine beetle 
(Dendroctonus monticolee Hopk.) in lodgepole pine since 1927. To 
study more intensively the effect of this infestation on a lodge- 
pole pine stand, a permanent sample strip 4% miles long and 66 feet 
wide was established in 1931 by personnel from the Coeur d'Alene 
forest insect field laboretory of the Bureau of Entomology. On 
this strip, which is considered representative of a large surround- 
ing area, there are practically no trees other than lodgepole pine. 
subject to mountain pine beetle atiack, und this timber species 
comprises 97.2 percent of the total number of trees. Beginning in 
1927 annual losses increased rapidly, reached their peak in 1931, 
showed a slight decrease in 1932, and were decidedly reduced in 
1933. By 1941 the largest trees had:all bean killed, heavy inroads 
made into those above the 8-—inch class, and it was already apparent 
that the larger the tree the more likely it was to be killed by the. 
beetles. The data elso indicated that the trees of smaller diameter 
were not favorable host material for the development of the bark bee- 
tle. Besices killing a largs' percentage of the trees, the beetles 
damaged many others. ‘Trecs damaged are confined to two classes of 
injury: The first, designated as "green-sided," include .trees ‘that 
still have a more or less narrow strip of living cambium on an un- 
attackec side; and a second class, designated as "pitched-out," are 
the trees that have drowned or repelled the attacking beetles by a 
co;ious flow of pitch. The. sreen-sided trees, although still living, 
are unfit for timber, and ate usually killed by secondary insects 
within a few years. The pitched-out trees can usually be put to the 
normal use of lodgepole pine. ~ 
By 1933 many of the trees of: smaller diameter had been killed 
or damaged by the bark heeti Lie end there were no undamaged trees 
larger than 11 inches in diameter: The Cea a tabulation shows 
the status of the stand. at Mes aan OY wal cats 
