262 WEST VIRGINIA EXPERIMENT STATION 



This trouble appears to be widely distributed over the coun- 

 try, and has received especial attention from Professor C. H. 

 Fernald of the Massachusetts Agricultural College in a recent 

 paper. 



THE PRINCIPAL INSECT FRIENDS OF THE SPRUCE, OR ENEMIES OF THE 



INSECT ENEMIES. 



The insects which are friendly or beneficial in their relation 

 to the spruce are those which prey upon the enemies and thus 

 prevent their excessive increase, and reduce the amount of in- 

 jury to the tree or its products. 



There are two classes of these beneficial insects, separated 

 according to their habits. One class which includes beetles 

 and their larvae attack and devour the adult, young, and eggs 

 of the injurious insects. While the other class which includes 

 the young of four- winged bees and wasps and two-winged flies, 

 attach themselves to the young of the injurious species, or 

 enter their bodies to absorb the liquids, thus causing the gradu- 

 al death of their victim. 



The list shows that considerably more beneficial than injuri- 

 ous species were taken from the spruce, but as a rule, the total 

 number of individuals of the injurious species is far greater 

 than that of their predatory and parasitic enemies, and were it 

 not for this check, they would multiply to excessive and devas- 

 tating numbers. 



PREDACEOUS BEETLES AND THEIR LARVAE. THE CLERIDS. 



The Clerids are perhaps entitled to occupy first rank among 

 the insects which prey upon the principal insect enemies of the 

 spruce. They are considerably larger than the insects upon 

 which they feed, and resemble the European bark beetle de- 

 stroyer (illustrated in the pine report) both in appearance and 

 general habits. 



The American Bark Beetle^ Destroyer 1 is nearest related. to 

 the European species, and is often quite common on the bark 

 of spruce trees infested with bark beetles. It is easily distin- 

 guished from the imported species by its red head and some- 



1 Tfianasimus dubiua, Fab. 



