378 WEST VIRGINIA EXPERIMENT STATION. 



on a given area on which all trees were killed, the line between 

 the dead and living timber being distinctly marked. 



It was often noted during my investigations of the work of 

 the destructive pine bark beetle, that many of these patches of 

 dead timber were not extended after the first attack. These sud- 

 den checks to the spread of the trouble from central points of in- 

 fection, were quite puzzling features. It was thought at first, 

 that it was due to the multiplication of parasitic and predaceous 

 enemies; but none of this class of enemies were subsequently 

 found at any time in sufficient numbers to make this seem pos- 

 sible. 



PARASITIC AND PREDACEOUS ENEMIES. 



In the early part of the season of 1892, but few parasitic or 

 predaceous enemies of Dendroctonus frontalis and of other as- 

 sociated species of bark beetle were found. Later in the sum- 

 mer they were more common, and in the fall they became quite 

 abundant. These enemies doubtless, exerted considerable in- 

 fluence in weakening the force of the attacking hosts of the de- 

 structive bark beetle and its allies ; but they can not be 

 credited with the extermination of this destructive species. 



CONCLUSION. 



In a review of all the evidence I have been able to bring to 

 bear upon the subject of the causes of the sudden extermina- 

 tion of Dendroctonus frontalis in this State, I am ready to 

 conclude that it was due to climatic conditions and the action 

 of one or more contageous diseases. 



