Circular No. 1 63. issued November 29, 1912. 



United States Department of Agriculture, 



BUREAU OF ENTOMOLOGY. 



L. O. HOWARD, Entomologist and Chief of Bureau. 



HYDROCYANIC-ACID GAS AGAINST HOUSEHOLD INSECTS. 



By L. O. Howard and C. H. Popenoe. 



Hj'^drocyanic-acid gas is one of the most effective remedies known 

 against various classes of insects. For more than 20 years it 

 has been the principal means of controlling scale insects on citrus 

 trees in California and is now in general use for the disinfection of 

 all deciduous nursery stock and other plant material for shipment, 

 and is one of the most eifective methods of ridding greenhouses and 

 cold frames of plant-lice, thrips, white flies, and various scale pests 

 which infest plants grown under glass.^ It has also become a stand- 

 ard remedy against the INIediterranean flour moth and other mill and 

 grain insects.- 



It has been fully demonstrated that this gas, which is very deadly 

 to all forms of animal life^ is, under proper precautions, an excellent 

 remedy for household insects. Probably its first use for this purpose 

 was in June of 1898, by Mr. C. L. Marlatt, of this bureau, against book 

 lice in the residence of an employee of the Department of Agriculture, 

 using the cyanid first at the ordinary strength employed on fruit 

 trees, then double, and finally quadruple the strength. The book lice 

 came from recently introduced leather-covered furniture, the cover- 

 ing of which -was so tightly fastened as to be almost, if not quite, 

 impervious to the gas, and the treatment was only partially succes- 

 ful. Another early use of this gas for household insects was in 1899 

 in San Francisco by the late Alexander Craw, then Chief Quarantine 

 Officer of the Board of Horticulture. In this case it was used against 

 bedbugs and in very small proportions. Two and one-half fluid 

 ounces of commercial sulphuric acid and 2^ ounces 98 per cent cyanid 

 of potassium were used in a house of several rooms, each containing 

 about 2,250 cubic feet of space. The rooms were closed for two 

 hours, then well aired. The operation was apparently successful. 



1 Refer to Circulars 37, 42, and 57 of the Bureau of Entomology and Farmer-s' Bul- 

 letin 172. 



' Refer to Circular 112, Bureau of Entomology, by F. U. Chittenden. 



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