44 



BULLETIN 737, U. S. DEPARTMENT OF ACRTCULTURE. 



in sealed glass tubes for a considerable time after exposure. The 

 eggs used were on leaf tobacco or in cells on microscope slides. Con- 

 trols were kept corresponding to the different stages. It was found 

 that adults and larva? become inactive after a few minutes exposure 

 to heat above 117° F.. but recover if the temperature is not kept 

 higher than 120° F. for a considerable length of time. An exposure 

 of 1 hour at 140° F. killed all stages of the beetle in small quantities 

 of tobacco but it was found that both larvae and pupae are more 

 resistant to heat while in the cells formed before pupation, the cells 

 serving as a protection. The results of several of the experiments 

 are given in Table VI. 



Table VI. 



-Effect of high temperatures on the tobacco hectic, 

 pertinents nt Clarksrillc, Tom., 1916. 



-Laboratorji e.r- 



Stage of insect. 



Ex- 

 posure. 



Temperature. 



Results. 



Remarks. 



Min. 



Max. 





Hours. 

 1 

 1 

 1 



1 



1 



2 



i 



1 

 1 



a 



l 2 

 i 



°F. 

 110 



110 

 117 



128 



128 



130 

 138 

 138 

 138 

 144 

 146 

 158 

 158 

 180 



°F. 



115 

 115 



120 



130 



131 



140 

 140 

 140 

 140 

 145 

 150 

 164 

 165 

 181 



Not effective 



...do 







In cigar. _ 





do 





do 



treatment. 

 Part of each stage killed; remainder 

 recovered. 



Eggs 



Effective 



do 





hatched normally. Eggs 1 day old. 



Eggs 



do 







do 



Do. 



Larvae and pupa? 



....do 





...do... 





Do 



...do 



Do. 



Do.. 



...do 



Eggs on leaf tobacco. 

 Do. 



Do. .. 



....do 



Do... 



....do 



Do. 













In these tests only a small quantity of the food substance was used. 

 The time required for treatment will therefore depend on the amount 

 and character of the food substance and the insulation furnished by 

 the container or wrapping material. The results of the numerous 

 tests made show that comparatively mild heat, if long continued, 

 is sufficient to kill all stages of the beetle. The temperatures found 

 effective are in no way injurious to certain classes of tobacco, which 

 in many cases are subjected to a much higher degree of heat in the 

 process of manufacture. 



STERILIZING TOHACCO WAREHOUSES BY MEANS OF STEAM. 



At Quincy, Fla., in July, 1913, an experiment was conducted by 

 Mr. D. C. Parman, of this bureau, and the writer in a large warehouse. 

 It is the custom of the managers to clean up and sterilize the ware- 

 houses as far as possible, usually by fumigation, before the new crop is 

 brought in. The warehouse used for the experiment was empty and the 

 owners wished to ascertain to what extent steam could be employed. 



