20 



long periods are not sufficient to destroy the vitality of the eggs of 

 the cigarette beetle and the freezing method is therefore not abso- 

 lutely preventive. 



In fumigating with carbon bisulphid use it at the rate of 1 pound 

 to 600 to 800 cubic feet of air space, pouring the liquid out into shallow 

 pans near the ceiling (the gas is heavier than air), first making the 

 building or compartment as tight as possible against leakage of the 

 gas. Small lots of infested tobacco can be fumigated in air-tight 

 boxes, using 1 ounce of carbon bisulphid to 50 to 60 cubic feet of air 

 space. Caution is advised in the use of this chemical on account of 

 its poisonous and inflammable nature. 



Hydrocyanic-acid gas is perhaps not so effective against stored- 

 product insects as carbon bisulphid, but has advantages in* cost and 

 ease of use. It is generated by placing cyanid of potassium in* sul- 

 phuric acid and water. It is lighter than air, and therefore, contrary 

 to the rule with carbon bisulphid, should be generated beneath. 

 Use in proportions of 1 ounce of 98 per cent pure cyanid, 1 fluid ounce 

 of commercial sulphuric acid, and 2 fluid ounces of water to 100 cubic 

 feet. Care must be exercised in using this treatment on account of 

 the very poisonous nature of the cyanid gas. 



Natural enemies. — A Pteromalus was bred from this species. 



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