60 BULLETIN 737, U. S. DEPARTMENT OF AGRICULTURE. 
Dosage 2.5 ounces per 100 cubic feet—This gave somewhat better 
results. In one experiment all stages were killed. In three experi- 
ments all unprotected adults and newly hatched larve were killed. 
Of the other stages approximately 11.8 per cent survived. | 
Dosage 3 ounces per 100 cubic feet—In four experiments this gave 
practically the same results as the 24-ounce dosage. 
Dosage 4 ounces per 100 cubic feet—In six experiments this dosage 
killed eggs, newly hatched larve, and practically all unprotected 
stages. Approximately 9 per cent of the larve, pupe, and adult 
stages within the pupal cells survived treatment. In one of the six 
experiments all stages were killed. 
Dosage 6 ounces per 100 cubic feet. eens the same results 
were shown in five experiments with the 6-ounce dosage. Eggs, newly 
hatched larve, and unprotected adults were killed. About 9.4 per cent 
of the other stages, mainly mature larve protected by dense substances 
or by the pupal cells, survived. In two of the five experiments all 
stages were killed. 
Dosage § ounces per 100 cubic feet.—In four experiments with an 
8-ounce dosage about 10 per cent of the protected stages survived. 
All adults which had emerged from the pupal cells and all eggs, 
newly hatched larve, and unprotected larve and pup were killed. 
In one experiment all stages were killed. 
The results obtained in other experiments made by Mr. Joseph 
Smith and the writer at Clarksville, Tenn., with both sodium cyanid 
and potassium cyanid in amounts from 1 ounce up to 8 ounces per 100 
cubic feet did not differ materially from those obtained with sodium 
cyanid in the series described. With both substances, in many in- 
stances, an increased dosage above 4 ounces per 100 cubic feet did not 
show a very decided increase in effectiveness, possibly due to the in- 
ability of the gas to penetrate dense food substances or pupal cells. 
DOUBLE FUMIGATION. 
Fumigation under most circumstances has not been found entirely 
' effective in sterilizing tobacco, as a few of the insects in either the — 
larva, pupa, or adult stage, protected by the pupal cells or by dense 
food substances, are apt to survive. In comparatively few of the 
experiments were the beetles completely exterminated. While a 
single treatment may be fairly satisfactory, since the few live stages 
left will require considerable time to increase to sufficient numbers 
to reinfest the tobacco badly, it is desirable under some circumstances 
to give a second treatment later in order to destroy the beetles remain- 
ing after the first treatment. This can be accomplished easily after 
the beetles have emerged from the pupal cell. With tobacco kept at 
ordinary room or summer temperatures the second fumigation should 
be given about two or three weeks after the first treatment, as by this 
