THE TOBACCO BEETLE. 



43 



of granulated smoking tobacco and passed during the regular course 

 of manufacture through the drying processses in use in a large fac- 

 tory where smoking tobacco is manufactured. ■ All stages of the beetle 

 were destroyed. In one of the driers a temperature of 180° F. was 

 reached, which is sufficiently high to sterilize the tobacco quickly 

 and effectively. 



In the New Providence factory the leaf tobacco, after treatment 

 with vaseline, is compressed into packing cases, placed in drying 

 rooms, and subjected to heat for some time. The maximum tem- 

 perature reached was found to be about 150° F. This process is used 

 for a certain grade of tobacco shipped to Africa and it is said that 

 little or no damage has ever been reported from mold or insect in- 

 jury. In the experiments made (Oct. 20-24, 1915) by Mr. A. C. 

 Morgan and the writer to determine the effect of the heating process 

 in destroying the different stages of the tobacco beetle, infested 

 tobacco was placed in the heating room and a continuous record of 

 the temperature obtained by means of a self-recording thermograph. 

 Humidity records were taken at the beginning and close of each 

 experiment. Part of the eggs used were on leaf tobacco on which 

 they had been deposited, and part in cells on microscope slides, and 

 control lots were kept for each of the different stages. In all of the 

 controls development was normal, but it was found that the tempera- 

 ture reached in the heating room resulted in killing all stages of the 

 beetle. The details of several of the experiments are given in 

 Table V. 



Table V. — Effect of heat on different stages of the tobacco beetle (Lasioderma 

 serricorne). Experiments at New Providence, Tenn., 1.915. 



Stage of insect. 



Rela- 



' tive 



humid- 

 ity. 



Tempera- 

 ture. 



Time 

 of ex- 



Results. 



Remarks. 





Eggs. 



Larvae. 



Tup SB. 



Adults. 



Min. 



Max. 







105 



114 

 32 



41 



10 

 42 



8 



10 

 10 



51 



75 

 28 



Percent. 

 38-40 



38-49 

 38-49 



°F. 

 97 



101 

 93 



°F. 

 140 



138 

 140 



Hours. 

 24 



48 

 72 



All stages 

 killed. 



do 



do 



Eggs 4 and 5 days old. 



Eggs 1 day old. 

 Eggs 1 to 5 days old. 



EFFECT OF HlfiH TEMPERATURES ON DIFFERENT STAGES OF THE TOBACCO BEETLE ■ 



LABORATORY EXPERIMENTS. 



At Clarksville, Tenn. (1916), numerous laboratory experiments 

 were conducted to determine the effect of high temperatures. The 

 incubators or ovens used in making the tests were fitted with water 

 jackets which permitted exposures to be made without much varia- 

 tion in temperature. The different lots were kept with suitable food 



