252 JOURNAL OF FORESTRY 



One set of experiments consisted of treating the infested wood in a 

 kiln held at different temperatures and for various periods. The 

 larvae were then chopped out and their condition noted. In the other 

 two groups of experiments, the naked larva; were exposed directly 

 to the different temperatures for definite periods. In one case' the 

 larvae were placed in water of determined and regulated temperatures, 

 and in the other the larvje were suhjected to the dry heat of an electric 

 oven. 



In each of these groups of experiments, the condition of the larvae 

 was rioted at the time the treatment was concluded. They were then 

 placed in small glass vials, corked with cotton and held until the larvae 

 turned dark, due to death, or until activity was noted. Consequently, 

 in some cases it was clearly evident that the larvae were dead a few- 

 minutes after removal from the wood while in other experiments or on 

 other specimens 48 hours were required to determine with certainty 

 the ultimate effect the treatment had on the larvae. 



In the kiln experiments the temperatures were thermostatically con- 

 trolled and were recorded by a Bristol recording thermometer. These 

 temperatures were also checked by maximum and minimum thermom- 

 eters. Previous experiments have shown that the temperature within 

 a piece of wood ultimately reaches approximately the dew point of the 

 surrounding air. Therefore, the relative humidity was held at lOQ 

 per cent so that the temperature in the wood might be the same as that 

 of the air surrounding the wood. It has also been determined by 

 previous experiments that heat moves through wood slowly — l-inch 

 stock coming to a uniform temperature in about an hour. In view of 

 the fact that the majority of the larvae were confined to the outer 1 

 inch of the specimens treated, it was concluded that an hour's treat- 

 ment at a certain temperature merely brought the wood surrounding" 

 the larvae up to the kiln temperature. 



Kiln runs were made at different temperatures and periods of time 

 starting at 160° F. for 1 hour and lowering to 110° F. for 70 hours. 

 In all tests above 128° F. the borers were killed in the experimental 

 runs in periods varying from 1 to 2 hours. Four hours at 120° F. 

 and 16 hours at 116° F. killed only about 50 per cent of the larvae,, 

 while 19 hours at 120° F. killed all the larva?. One hundred per cent 

 mortality was also secured in 45 hours at 116° F. and in 70 hours at 

 110° F. 



