THE GENUS DENDROCTONUS. 27 
and mines, and kill their victims by inserting their beaks into their 
bodies. 
The so-called robbers (see fig. 30) consist of large bark-boring 
grubs or larva? of long-horned beetles, a which sometimes rob the 
barkbeetle larva* of their food supply or kill them outright, by 
destroying the inner bark before the broods of barkbeetles have 
completed their development. These, however, do not occur so 
commonly with the more destructive barkbeetles as with those 
which, like the bark-boring grubs, are in the bark as the result, and 
not the cause, of the dying condition of the tree. 
While some of the Dendroctonus beetles have numerous insect 
enemies, others have comparatively few. Some of the smaller species, 
like the southern pine beetle, which often occupy the thin bark on the 
upper portion of the trunk and branches of the larger trees, and 
sometimes on young trees, have many parasitic enemies, while others 
of the small species, as 1, 2, and 5, and the larger species, such as the 
Black Hills beetle and the Douglas fir beetle, which usually occupy 
the thick bark, have none at all, or very few. 
So far as determined, the southern pine beetle has 1 1 parasitic and 
about an equal number of predatory enemies; the eastern spruce 
beetle has 5 parasitic and 4 predatory enemies, and the eastern larch 
beetle 6 parasitic and 2 predatory enemies. Of the western species 
the mountain pine beetle is the only one on which a parasite has been 
found, but there are four or five predators common to all, which evi- 
dently exert quite an important influence in protecting the forests of 
some sections. With a little assistance on the part of the owner of 
the forest, this class of beneficial insects will exert a much more power- 
ful influence in preserving a desirable balance among the contending 
forces, and thus prevent destructive outbreaks of the beetles. This 
balanced condition appears to prevail at the present time within the 
range of the southern pine beetle, and with proper attention to local 
outbreaks of the beetles it could be maintained. However, this whole 
subject of parasites and predatory enemies of forest insects and their 
economic relations is one which has not as yet received the attention 
it deserves. Mr. Fiske gave the matter considerable attention during 
his field work in forest insect investigations, but his detail to another 
branch of the Bureau prevented him from continuing it. 
BIRDS. 
Wherever the Dendroctonus beetles have been found in standing 
timber the work of woodpeckers has been more or less common, and in 
some trees quite a large percentage of the beetle broods has been 
destroyed by the birds. The evidence gathered in Maine a few years 
a Family Cerambycidse. 
