60 BULLETIN 731, 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 larva? 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 2^-ounce dosage. 



Dosage 4 ounces per 100 cubic feet. — In six experiments this dosage 

 killed eggs, newly hatched larvae, and practically all unprotected 

 stages. Approximately 9 per cent of the larvae, pupae, 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. — Practically the same results 

 were shown in five experiments with the 6-ounce dosage. Eggs, newly 

 hatched larvae, and unprotected adults were killed. About 9.4 per cent 

 of the other stages, mainly mature larvae protected by dense substances 

 or by the pupal cells, survived. In two of the five experiments all 

 stages were killed. 



Dosage 8 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 larvae, and unprotected larvae and pupae 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 



