356 
Jounml of Agricultural Research v 0 i. xxvm, No. 4 
When using a good grade of either carbon disulphide or hydrocyanic-acid gas 
in a gas-tight fumigator, at a sufficiently high temperature, and with a sufficiently 
long exposure, it is entirely possible with one fumigation to kill all the weevils, 
in all stages, either among or within beans or cowpeas. This, however, will of 
course not prevent a reinfestation if weevils have access to the fumigated seeds. 
Small quantities of beans may be thoroughly fumigated with a minimum of 3 
pounds of carbon disulphide per 1,000 cubic feet at a temperature of 58° F. or 
higher for a period of 24 hours or with 1J pounds for 48 hours; with two pounds 
of liquefied hydrocyanic acid for 48 hours at 70° F. or higher or with 1.3 pounds 
for 90 hours; with hydrocyanic-acid gas generated from 3.4 pounds of sodium 
cyanide by the pot method at 70° F. for 48 hours or from 1.8 pounds of sodium 
cyanide for 90 hours. 
Large quantities of beans require a longer exposure or a greater quantity of 
the fumigant, the latter being preferable. When beans are fumigated with 
hydrocyanic-acid gas they should be given an exposure of at least 48 hours. 
When either carbon disulphid or hydrocyanic-acid gas is used as a fumigant, 
the weevil Bruchus obtectus is most easily killed in the young larval stage just 
after hatching and just before entrance into the bean. Emerged adults, eggs, 
and young larvae just after having entered the bean succumb to fumigation in 
the order named, while it appears that unemerged adults and pupae are hardest 
to kill. It appears, however, that the depth to which the weevil is buried in 
the bean is important as affecting its ability to withstand fumigation. 
Stages of Bruchus quadrimaculatus are most easily killed in the following order: 
Emerged adults, eggs, larvae that have not entirely left the chorion, and young 
larvae just inside the seed; the other stages appear to be effected almost equally* 
The larvae that are deepest in the cowpeas survive longer than other larvae. 
This accounts for the fact that the prepupae appear to be a little more resistant 
than the other stages. 
LITERATURE CITED 
(1) Hinds, W. E. 
1917. carbon disulphid as an insecticide. U. S. Dept. Agr. Farmers' 
Bui. 799, 21 p. 
( 2 ) Krall, J. A. 
1914. THE COWPEA WEEVIL (PACHYMERUS CHINENSIS). Okla. Agr. Exp. 
Sta. Circ. 31, 8 p. 
(3) Metcalf, Z. P. 
1917. lime as an insecticide. Jour. Econ. Ent. 10: 74r-78, illus. 
(4) Osborn, H., and Mally, C. W. 
1896. THE FOUR-SPOTTED PEA WEEVIL. (BRUCHUS QUADRIMACULATUS 
fabr.). Iowa Agr. Exp. Sta. Bui. 32: 386-394, illus. 
(5) Paddock, F. B., and Reinhard, H. J. 
1919. the cowpea weevil. Tex. Agr. Exp. Sta. Bui. 256, 92 p., illus. 
( 6 ) Pettit, R. H. 
1906. THE FOUR-SPOTTED BEAN WEEVIL (BRUCHUS QUADRIMACULATUS). 
Mich. Agr. Exp. Sta. Bui. 244: 100 - 101 , illus. 
(7) Wade, O. 
1919. THE FOUR-SPOTTED COWPEA WEEVIL (BRUCHUS QUADRIMACULATUS 
fabricius) . Okla. Agr. Exp. Sta. Bui. 129, 14 p., illus. 
