FUMIGATION OF BEAN WEEVILS, BRUCHUS OBTECTUS 
SAY AND B. QUADRIMACULATUS FAB . 1 
By A. O. Larson 
Assistant Entomologist, Stored-Product Insect Investigations , Bureau of Entomology , 
United States Department of Agriculture 
INTRODUCTION 
In the course of the bean weevil investigations carried on in California during 
the last four years, the writer has had an opportunity to make observations on 
the methods of fumigation and their effectiveness when applied to bean weevils. 2 
He has carried on fumigation experiments using carbon disulphide, hydrocyanic- 
acid gas obtained from liquefied hydrocyanic acid, and hydrocyanic-acid gas 
generated by the pot method, the amounts of beans fumigated varying from only a 
small quantity to 300 centals, or 30,000 pounds, at a time. 
Liquefied hydrocyanic-acid gas, as used in these experiments, was the com¬ 
mercial hydrocyanic-acid gas. This material contains not less than 96 per cent 
actual hydrocyanic acid, and is free from alkalies, ammonia, chlorine, hydrochloric 
acid, and nitric acid. For economy of space, this material is designated as Liq. 
HCN in the tables of results. 
The material used in the pots for the generation of hydrocyanic-acid gas was 
commercial sodium cyanide labeled 98-99 per cent pure and commerical sulphuric 
acid 66° B. 
The beans, California Pink and Red Mexican, and the cowpeas, Large Blackeye, 
Red Ripper, and Black-Spotted or Holstein, used in these experiments, are 
thought to be typical examples of beans and cowpeas, and it is believed that a 
fumigant will penetrate other varieties in approximately the time required to 
penetrate these. The bean weevils, Bruchus obtectus Say, were contained within 
and among the California Pink, Red Mexican, and Large Blackeyed cowpeas, 
while the four-spotted cowpea weevils, B. quadrimaculatus Fab., were within and 
among the cowpeas only. 
In these experiments carbon disulphide was used in quantities varying from 
1.5 to 31 pounds per 1,000 cubic feet, at temperatures of from 52° to 82° F., and 
with exposures of from 1 to 90 hours, as well as in a vacuum of 29 inches. Lique¬ 
fied hydrocyanic acid was used in amounts from 1.3 to 3.5 pounds 3 per 1,000 
cubic feet at temperatures of from 58° to 92° F. for lengths of time varying from 
24 to 90 hours. In generating hydrocyanic-acid gas by the pot method, from 
1.8 to 3.4 pounds of sodium cyanide was used per 1,000 cubic feet at 67° to 84° F. 
for from 48 to 90 hours. _■__ 
1 Received for publication April 19,1924. 
2 The writer began the bean weevil investigation in 1919 under the direction of Dr. E. A. Back, ento¬ 
mologist in charge of stored-product insect investigations of the Bureau of Entomology, United States 
Department of Agriculture. In the fumigation work he has been assisted at various times by E. Nelson, 
B. Smit, and A. H. Amis, all of whom have rendered assistance in various ways. 
He wishes to thank especially D. B. Mackie, of the State department of agriculture of California, Sacra¬ 
mento, Calif., C. L. Main, of the Puente Milling & Warehouse Co., Puente, Calif., and E. R. Hulbirt, of 
the Owl Fumigation Corporation, Azusa, Calif., for their valuable cooperation, and for the services they so 
courteously rendered. 
8 In citrus fumigation 18 cc. of liquefied hydrocyanic acid is considered to be the equivalent of 1 ounCg 
of sodium cyanide, but 20 cc. is more nearly the equivalent at 60° F. At 60° F., 642 cc. of liquefied 
hydrocyanic acid weighs 1 pound; at 70° F., 650 cc. of liquefied hydrocyanic acid weighs 1 pound; at 80° 
F., 659 cc. of liquefied hydrocyanic acid weighs 1 pound. 
Journal of Agricultural Research. 
Washington, D C. 
(347) 
Vol. XXVIII, No. 4 
April 26,1924 
Key No. K-135 
