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WEST VIRGINIA EXPERIMENT STATION. 



contribute to their welfare and help counteract the damage 

 done to them by their enemies. 



INSECT FRIENDS OF SCOLYTIDS. 



The principal friends of Scolytids consists of parasites, of 

 their predaceous and parasitic enemies, which are known as 

 secondary parasites. These are principally minute, four winged 

 gnats belonging to the family Chaicididae. They deposit their 

 eggs in or on the adults, larvae or pupae of the enemies of the 

 Scolytids and destroy them in the same manner as the Scoly- 

 tids are destroyed by their parasites This class of insects are 

 among the best friends of the Scolytids in preventing the rapid 

 increase of their enemies. 



Caterpillars which defoliate trees and thus weaken their 

 vitality, offer favorable conditions for attack by Scolytids and 

 may thus be classed among their insect friends; as may certain 

 plant lice which attack the foliage of pine and other trees; and 

 also certain wood-boring caterpillars and grubs which kill the 

 twigs and branches on living trees, or cause a diseased condi- 

 tion of the entire tree. 



Man as a friend of scolytids. Man, especially civil- 

 ized man, is among the best friends of Scolytids in 

 causing favorable conditions for their multiplication. 

 In the primitive forests of this country all but a few 

 species of the Scolytids necessarily depend upon occasional 

 outbreaks of destructive species and other natural conditions 

 for their supply of suitable material in which to breed; but 

 upon the advent of civilized man, suitable material is furnished 

 in the greatest abundance in the girdled trees in the settlers' 

 clearings or in the logs, stumps, and tops of trees felled at first 

 for building material and subsequently for commercial products. 

 In opening up clearings and highways in and through the 

 primitive forests of conifers the most lavorable conditions were 

 offered for the starting of invasions of destructive bark beetles. 



FOREST FIRES. 



Forest fires, directly or indirectly due to man's influence 

 offer both favorable and unfavorable conditions for the exist- 



