18 N. J. Agricultural Experiment Stations, Bulletin 355 



From this tabic it will be seen that the minimum dose for 

 plant lice experimented with (Macrosiphum rosae), lies in the 

 neighborhood of 0.00015 to 0.0002 gm. HCN per liter, depending 

 upon the temperature. Checks at 40° F. and at 100° F. were run 

 in all the experiments with minimum dosage, and in no case was 

 any mortality observed. 



TABLE I 

 Effect of Different Dosages of Hydrocganic Acid Gas on Plant Lice 



The failure to kill the aphids at a low temperature will ex- 

 plain the rather high percentages of HCN gas necessary to pro- 

 duce killing effects in greenhouses, where as a matter of safety 

 to the plants during fumigation the temperature is kept low. 

 But it will not explain the great difference in the amount of gas 

 necessary to kill in these minimum dosage experiments, and the 

 amount found necessary to produce killing in greenhouses. 



