THE TOBACCO BEETLE. ' 59 



For every 100 cubic feet of space use multiples of this formula to 

 secure the dosage desired. The dosage used may be the same as with 

 sodium cyanid. It will be noted that the amount of acid required 

 with potassium cyanid is less than with sodium cyanid. 



In using either potassium cyanid or sodium cyanid for fumigat- 

 ing, a greater amount of water than that given in the formulas should 

 not be used, as any quantity of water above 3 fluid ounces for each 

 ounce of cyanid results in a smaller yield of hydrocyanic-acid gas. 



In preparing chemicals for fumigation the cyanid is weighed, and 

 the acid and water are measured. The time of exposure has been 

 found to be an important factor in fumigation and it is not advis- 

 able to make the time less than 24 hours, unless the vacuum process 

 of fumigating is employed. A comparatively small dosage with a 

 long exposure appears to be as effective as is a heavier dosage with a 

 shorter exposure. 



SUMMARY OF RESULTS OF FUMIGATION EXPERIMENTS. 



A brief summary of the average results obtained in a series of 34 

 fumigating experiments with material infested by the tobacco beetle 

 follows. Different dosages of sodium cyanid varying from 1 to 8 

 ounces per 100 cubic feet of space were used. The time of treatment 

 was 24 hours. The tests were made during July, August, and Sep- 

 tember, the maximum temperatures varying from 82° to 92° F. and 

 the minimum temperatures from 42° to 72° F. All stages of the 

 beetle in leaf tobacco, in different classes of manufactured tobacco, 

 and in pressed yeast cake, were utilized. Part of the eggs, for con- 

 venience in making examinations, were placed in cells on microscope 

 slides, and part were located on the original leaf tobacco on which 

 they had been deposited. The eggs used were from 1 to 6 days old. 

 Multiples of the 1-1^-3 formula were used with the sodium cyanid. 

 The results obtained with different dosages were as follows : 



Dosage 1 ounce per 100 cubic feet of space. — In three experiments 

 only a few egg^ hatched. In these embryonic development was nearly 

 complete at the time of treatment. Newly hatched larvae were nearly 

 all killed, about 4 per cent in dense tobacco survived, and of the 

 other stages, including adults, pupae, and fully developed larvae, 

 about 22.3 per cent survived treatment. 



Dosage 1.5 ounces per 100 cubic feet of space. — In four experiments 

 eggs and newly hatched larvae were killed. Approximately 21 per 

 cent of other stages survived treatment. The adults remaining alive 

 were mainly those which had not emerged from the pupal cells. 



Dosage 2 ounces per 100 cubic feet. — This treatment destroyed eggs 

 and newly hatched larvae. In four experiments 18.6 per cent of the 

 other stages survived. 



