ASPEN IN THE CENTRAL ROCKY MOUNTAIN REGION 17 
One of the cecidomyid group of gall insects also does considerable 
damage to aspen buds in April and May, stunting the trees but not 
killing them. 
One of the plant lice, Chaitophorus sp r does some damage by 
killing back tender shoots, although the trees are not seriously 
hurt. 
In Montana a number of insects infesting broad-leafed trees in- 
clude aspen in their attacks, but they do not often damage the aspen 
severely. Among these are Lina scripta, a chrysomelid beetle simi- 
lar to the elm leaf beetle; Onychagrotes rUeyana, a noctuid moth 
larva, which works in the green bark; larva of Euvanessa antiopa and 
Aglais j-album; and the buprestid beetles Chrysobothrts femorata 
and Agrilus am&ius. These are doubtless found in regions south of 
Montana as well. 
In Colorado severe local attacks by a tent caterpillar, Malacasoma 
fragilis, have been noted, but appearances give the impression that 
natural enemies usually hold this menace in check. 
The investigations of the Bureau of Entomology throughout the 
Rocky Mountain region have indicated that the aspen borer (Saperda 
calcarata) and A grilles anxius are among the most important insects 
attacking the aspen. 
A common ambrosia beetle, Trypodendron (Xyloterus) retusum, 
which has been noted especially on the Cache Forest in Utah, attacks 
the wood of weakened and dying aspen trees. 
MAMMALS 
Mammals are the chief living enemies of aspen. Sheep are by 
far the worst, followed by cattle, and wild rodents such as rabbits, 
mice, and gophers. 
Sheep grazing is very frequently destructive to aspen sprouts to 
such an extent that, if continued longer than a rotation of aspen, 
it means the extinction of the type in many localities. This phase 
of aspen management has been covered thoroughly by Sampson {12) , 
and his findings appear to apply to all the Kocky Mountain region. 
The most important result of these studies was the discovery that 
sheep grazing is especially destructive on clean-cut areas, and that 
if it is continued three consecutive years all aspen sprouts will be 
absolutely killed out. Sheep do not reach higher than about 42 
inches, however, and protection for a long enough period to allow 
a certain minimum number of the sprouts to pass this height is all 
that is necessary. This will vary with the rate of height growth 
and the number of sprouts per acre. 
Cattle grazing is less uniform and the damage depends more upon 
the intensity of grazing and the nature of the forage on the area. 
In some places damage is negligible and in others it is very severe. 
The degree of protection will necessarily vary with grazing condi- 
tions, and, where these are very bad, complete protection may be 
needed until the aspen sprouts are entirely safe from destruction by 
browsing, or until the sprouts are 55 to 60 inches tall. 
Sampson's publication presents practically all data available along 
this line. Table 9 has been prepared to show the percentage of 
2023°— 25 2 
