296 Insectichles 



"It is through absorption into the insect tissues of the volatile portions of kero- 

 sene, gasoline, creolin, pyi-ethnim and such contact insecticides that they mainly 

 become effective agents against insects. Vapors from these insecticides enter the 

 tissues and become effective long before the liquids as such have time to penetrate 

 the chitin. Kerosene, miscible oils, etc., are able to enter the spiracles and tracheae 

 of insects even when a 'closing apparatus' is present; but the comparatively 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 disulphid, creolin, 

 and the i-est upon insects are very similar to the effects of the vapor of ether. The 

 nervous system seems to be especially affected. Small amounts of such vapors 

 produce, at first, more or less excitement; then a period of uncertain movements; 

 and finally in larger amounts anesthesia 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 dioxid, ammonia and hydrocyanic 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 disulphid, carbon dioxid, kerosene, gasohne, 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 off from the tissues again — but 

 not quite as readily as they were absorbed. 



"Starvation, serious mechanical injury, and ammonia gas were all foimd to reduce 

 the value of the respiratory quotient below the value given when healthy strong 

 insects are breathing pure air. 



"The vapors of gasohne, carbon disulphid, kerosene and To-bak-ine {i.e. nicotin), 

 when present in sufficient amounts to bring the insects 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 dioxid excreting activity. The insects tried could contiime to give 

 oft' small amounts of carbon dioxid when no oxygen was present to be taken up, as 

 when they were kept in tested nitrogen, hydrogen, or carbon dioxid. 



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

 carbon disulphid and the like, after absorption into the insect body, become mainly 

 effective through some tendency their presence 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 mai-gin of a 

 scale insect like the San Jose scale, arc the important properties that make it efficient 

 as a scalecide." Expt. Stat. Record, 1912. 



" A contribution to our knowledge of insecticides," C. T. McCUntock, E. M. Hough- 

 ton and H. C. Hamilton {Rpt. Mich. Acad. Sci. x (1908), pp. 197-208, pi. 1, reprint) 



"The work reported in this paper has to do with contact insecticides onlj\ . . . 



"The insecticidal, germicidal, and toxic values (for higher animals) have httle or no 

 correlation. It is possible to determine the relative strength or value of insecticides 



