26 THE SCOLYTID BEETLES. 
of such trees or convert them into lumber and burn the slabs before 
the insects begin to emerge. "Winter cutting of living, healthy tim- 
ber is much to be preferred when species with a single generation, 
like the mountain pine beetle, Douglas fir beetle, or the spruce beetles, 
are present, because dining the following summer the stumps and 
slash will serve to attract the beetles away from the living trees. 
And since the broods would remain in the bark during the following: 
winter they can then be destroyed by burning the slash any time 
dining the following fall or winter. In the Southeast and in the 
Rocky Mountain region, however, when species with more than one 
generation annually are present, it may be necessary to burn the 
winter slash before the first of July, to destroy the broods of the 
first generation winch develop from eggs deposited during May or 
June. 
NATURAL ENEMIES OF THE BEETLES. 
Were it not for the natural checks and control of some of the 
insect enemies of forest trees, the destruction of the forests would 
evidently be far more continuous and complete, but imder the 
existmg warfare between the trees and the destructive beetles and 
between the beetles and their own enemies, a more or less balanced 
condition in nature is preserved, so that it is only under exceptional 
conditions that a species of tree or a species of insect is extermi- 
nated. 
IXSECTS. 
The insect enemies of the destructive beetles consist of parasites, 
predators, and robbers. The parasites are small wasplike insects. 
The adults lay their eggs on, in, or near the beetle larvae, and the 
minute maggotlike larvae of the parasite, situated either internally 
or externally, feed on the body fluids and thus cause the death of 
their victims. W lien the parasite larva reaches its fall development 
it either changes to a free papa in the mine of its victim or makes 
a cocoon in which it goes through its transformation. Therefore 
the presence of certain of the parasitic enemies of the beetle larva? 
is indicated by the presence of their cocoons in the mines, even after 
their victims have been destroyed and they themselves have emerged. 
The principal predators consist of certain adult beetles and their 
larva? 6 (see fig. 32), the adults often feeding on the adults of the 
destructive beetles before or after they enter the bark, and the 
larvae feeding on the broods of the beetle larva 1 in the bark. 
There is another class of predatory enemies of the beetles among 
the true bugs, which follow the beetles and larva 1 into their galleries 
a Order Hymenoptera. families Braconida?, Chalcididae, etc. 
b Order Coleoptera. families Cleridse, Histeridae. Tros:ositidse. Colydiidae, etc. 
c Family Anthocoridae.j 
