594 STATE BOARD OF AGRICULTURE. 



sene, miscible oils, etc., are able to enter the spiracles and tracheae of 

 insects even when a "closing apparatus" is present; but the compara- 

 tively rapid influence which such insecticides exert does not come from 

 the plugging of the tracheae alone. 



The general effects of vapors from gasoline, kerosene, carbon disul- 

 phide, creolin and the rest (see page 19) upon insects are very similar to 

 the effects of the vapor of ether. The nervous system seems to be espec- 

 ially affected. Small amounts of such vapors produce, at first, more or 

 less excitement; then a period of uncertain movements; and finally in 

 larger amounts anaesthesia or narcosis. The respiratory activity is 

 usually increased until after the insects become deeply affected, and it 

 is then depressed. 



Certain gases and vapors (e. g. sulphur dioxide, ammonia, and hydro- 

 cyanic acid gas), when present in respired air continue to be absorbed 

 by insects while they are alive. For the most part, these gases are not 

 given off when the insects are exposed to fresh air but become rather 

 firmly fixed within the tissues. 



Insect-tissues quickly become saturated with any certain percentage 

 of the vapor of carbon disulphide, carbon dioxide, kerosene, gasoline 

 or similar vapor and no more (at that percentage) is taken up. Then 

 when the insects are exposed to pure air, practically all of such vapors 

 or gases are given oft" from the tissues again — but not quite as readily 

 as they were absorbed. 



Starvation, serious mechanical injury, and ammonia gas were all 

 found to reduce the value of the respiratory quotient below the value 

 given when healthy strong insects are breathing pure air. 



The vapors of gasoline, carbon disulphide, kerosene, and To-bak-ine 

 (i. e.. Nicotine), when present in suflicient amounts to bring the in- 

 sects near death, cause the value of the respiratory ratio to rise above 

 the value given by healthy, strong insects breathing pure air — i. e., 

 these vapors depress the activity of oxygen absorption more than they do 

 the carbon dioxide excreting activity. The insects tried could continue 

 to give off small amounts of carbon dioxide when no oxygen was present 

 to be taken up, as when they were kept in tested nitrogen, hydrogen, 

 or carbon dioxide. 



The evidence gathered seems to indicate that the vapors of gasoline, 

 kerosene, carbon disulphide and the like, after absorption into the 

 insect-body, become mainly effective through some tendency their pres- 

 ence exerts to prevent oxygen absorption by the tissues. 



Lime-sulphur is a special rather than a general contact insecticide. 

 Its strong, persistent reducing power, and its ability to soften the 

 wax about the margin of a scale insect like the San Jose scale are the 

 important properties that make it efficient as a scalecide. 



