460 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 5 



The optimum conditions for attack seem to be following fires occur- 

 ring early in the growing season. At such times the killing power of 

 fire is at its highest. The moist condition of the wood causes fermen- 

 tation and a rise of temperature. This favors the rapid gro^^i:h of 

 the larvae, giving them time to become well established before season- 

 ing of the wood and cold weather interferes. 



On a large area burned about the middle of June, infestation by the 

 last of August was so severe that the ground under the trees was white 

 with the dust from the borings, which could be seen drifting to the 

 ground like a light snow. The gnawing of the larvae sounded like the 

 croaking of innumerable frogs. An area close by burned in March 

 was much less severely infested. 



Rate of Destruction. Foresters and lumbermen in the Black Hills 

 recognize the fatt that fire-killed timber is generally worthless after 

 it has stood two years. The relation of the season of the fire to the 

 rate of destruction is not so well understood. 



Timber killed just before the flying season will be practically worth- 

 less in fifteen months, or by the following fall, while timber killed 

 after the growing season may not be as badly riddled after two years 

 and a half. A close study of the rate of destruction would be of great 

 value. 



An attempt is made to express some of the facts regarding infestation 

 and destruction graphically. The curves shown are for the most part 

 relative as we do not possess sufficient data to make them entirely 

 specific. The table derived partly from Curve III., would, if accu- 

 rately worked up, be of value, by showing the time necessary to effect 

 the injury and destruction of timber killed at different seasons. 



. Influence of Site on Severity of Attack. Wood borers prefer moist 

 wood, and are therefore most frequent in localities where the wood is 

 damp, such as in canyons, on steep north slopes etc., where there is 

 protection from the sun and winds. On the tops of ridges exposed 

 to wind and sun timber seasons quickly, and infestation is there- 

 fore often slight. The writer has examined timber from such locali- 

 ties that was unaffected by borers although it had been dead for 

 several seasons. The proximity of a burned to an infested area is 

 favorable for the spread of the pests. 



These facts should be kept in mind in projecting a cutting in a 

 recently burned area to prevent infestation. Timber in damp situa- 

 tions and that near infested areas should be removed or barked first. 



Natural Checks. The large amount of dead timber scattered through 

 the Black Hills as a result of the beetle invasion and the numerous 

 fires have given a splendid and not neglected opportunity for wood 

 borers. 



