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 during 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 

 during 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 Jul} T , to destroy the broods of the 

 first generation which 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 under the 

 existing 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. 



INSECTS. 



The insect enemies of the destructive beetles consist of parasites, 

 predators, and robbers. The parasites are small w^asplike insects. a 

 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. When the parasite larva reaches its full development 

 it either changes to a free pupa 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 larvae 

 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 

 larvae 5 (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 larvae in the bark. 



There is another class of predator}^ enemies of the beetles among 

 the true bugs, c which follow the beetles and larvae into their galleries 



« Order Hymenoptera, families Braconidse, Chalcididse, etc. 



6 Order Coleoptera, families Cleridae, Histeridae, Trogositidse, Colydiidse. etc. 



c Family Anthocoridae. 



