TOXICITY OF HYDROCYANIC ACID. 2O5 



tr 



r 

 6 



s , 



_J 



cr 

 x 

 h 



LJ 



I 



KT ZO 50 fO ,50 60 



EXPOSURE IN MINUTES 



FIG. 4. Curve showing the relation of concentration of HCN to length of 

 exposure and the effect of temperature upon the toxicity of HCN to Thrips tabaci- 

 Solid line 25 C.; broken line, 30 C.; dotted line, 20 C. 



TEMPERATURE. 



It is known that metabolic processes increase with increase in 

 temperature. With an increase in metabolic activities, we would 

 expect an increase in the susceptibility of the insect to HCX. 

 That such appears to be the case is shown in Figs. 2, 3 and 4. 

 It may be noted from these figures that the effect of temperature 

 is more pronounced with the shorter exposures. 



Throughout the experiments on aphids, it was noted that the 

 young organisms and the winged adults were more susceptible 

 than the wingless adults. These results coincide with Child's 1 

 idea that the physiologically young organisms have a higher 

 rate of metabolism than the older animals and are more sus- 

 ceptible to cyanide. In the case of thrips, however, the adults 

 seem to be easier to kill than the young. 



1 Child, "Senescence and Rejuvenescence," Chicago University Press, 1915. 



15 



