TEMPERATURES FATAI, TO LARV^ 



253 



In the water experiments the larvje were first chopped out of the 

 wood and, if ahve and active, were then submerged and held at 

 definite known temperatures for various periods. Temperature and 

 time periods varying from 1 minute at 117° F. to 60 minutes at 125° 

 F. were used. Ten minutes' exposure at 125° F. killed only 50 per 

 cent of the larvae, while 1 hour killed 75 per cent. Thirty minutes at 

 120° F. also killed 75 per cent, while 2^ hours at the same temperature 

 killed 100 per cent. All the foregoing temperatures caused cessation 

 of activities within 2 minutes. 



In the dry-air experiments the naked larvae were held at a desired 

 temperature for a definite period. An electrically heated oven was 

 used for these tests and its temperature was determined by an enclosed 

 mercury thermometer which could be read from the outside. Tempera- 

 tures from 116° to 123° F. and time exposures from 2 minutes to 1 

 hour were used. Ten and one-half minutes' exposure at 120° F. re- 

 sulted in death, as well as 122° F. for 5 minutes and 125° F. for 2 

 minutes. On the other hand, 120° F. exposure for 2, 3, and 4- minutes 

 did not kill the lar^^se; nor did 118° F. for 16 minutes. This last 

 temperature (118° F. for 16 minutes) did not cause cessation of activ- 

 ities. All temperatures of 120° F. or above caused cessation of activ- 

 ities after 2 minutes' exposure. 



CONCLUSIONS 



The outstanding deductions from this study were that the larvae 

 of the red-headed ash borer are killed in any kiln process which can be- 

 considered practical for the seasoning of ash, regardless of the thick- 

 ness. Even temperatures as mild as those used in Schedule 2, Specifi- 

 cation 20,500 A, Bureau of Aircraft Production, which range from 

 105° to 135° P., are fatal to them. Subjecting infested material to 

 a temperature of 116° F. for 15 hours resulted in 100 per cent death 

 of the larva?. Temperatures of about 125° to 130° F. will kill the 

 larvae within an hour after the wood becomes heated through. 



Dry heat is fatal to the larvre at a lower temperature than hot 

 water for the same period. 



Water at 125° F. for an hour was fatal to only 75 per cent of the 

 larvae treated, while dry air at 125° F. resulted in 100 per cent death 

 in 2 minutes. The time required to produce 100 per cent death in 

 dry air at 120° F. was lOyi minutes, while the same eft'ect was pro- 

 duced in water only after 2^ hours. These time limits are not to be 



