366 Forestry Quarterly. 



adults are flying. The further removed from this period the fire 

 comes the less will be the strength of the beetle attack, since the 

 wood has more chance to dry out and the bark to become de- 

 tached. 



The optimum conditions for attack seem to be following fires 

 occuring early in the growing season. At such times the killing 

 power of fire is at its highest. The moist condition of the wood 

 causes fermentation and a rise of temperature. This favors the 

 rapid growth of the larvae, giving them time to become well es- 

 tablished before seasoning of the wood and cold weather in- 

 terferes. 



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 fact that fire-killed timber is generally worth- 

 less 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 

 worthless 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 in- 

 festation 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 accurately 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 therefore often slight. The writer has ex- 



