EXPERIMENT STATION BULLETINS. 545 



liours entire recovery resulted. Several beetles were tried in this way. 

 All recovered so as to walk and feed. They were kept under observa- 

 tion for five days. When the beetles were dipped in the same manner in 

 kerosene or gasoline there was no recovery. Death was certain and 

 comparatively rapid — especially so in the case of gasoline. *01eic acid 

 is not equally harmless to all insects nor is it as harmless as water to 

 any, but it is a heavier oily substance than kerosene and as capable of 

 plugging the tracheae in the beetle, Passahis cornutus, as the latter 

 oil. There could be but one conclusion. Oil in the tracheae (depend- 

 ing upon the amount present) interfered with the passage of air, but 

 the rapid death from kerosene and gasoline was not due to plugging of 

 the tracheae alone. 



Furthermore, it was noticed that air saturated with the vapor of 

 gasoline at 72° F. killed most insects nearly or quite as rapidly as the 

 liquid itself. The presence of a very small amount of carbon disulphide 

 vapor in the air kills insects, as is well known. Death from the vapor 

 of these liquids could scarcely be due to a plugging of the tracheae. 

 Neither might it be due, alone, to the fact that the vapor dilutes the 

 air of its oxygen, since experiments confirmed Sorg's early conclusion 

 in 1805 that some insects may use practically all the oxygen from a 

 limited quantity of air. Indeed, as will be shown later, Passahis cor- 

 nutus can extract all the oxygen from a limited supply of air before 

 death results. Tests were tried further with the vapors of kerosene, 

 benzol, to-bak-ine, hydrocyanic acid, chloroform, special kreso dip, 

 creosote, aniline oil, pyrethrum, carbon disulphide, pyro cresol, creolin, 

 chloro-naphtholium, sulphur dioxide, common ether, neutral oil kreso, 

 crel oil and zenolium. It was found that the vapors of all these in- 

 secticides affect insects, and at temperatures ranging from 70° to 84° 

 F., the vapors from the more volatile substances kill many kinds of 

 insects. CeutJiophilus sp. was especially sensitive. (Miscible oils, be- 

 sides containing a varying amount of some volatile body, are also more 

 or less alkaline.) Any vapor coming from peanut oil, castor oil, oleic 

 acid and the common soaps showed little or no effect at the temperatures 

 named. Kesults of some of these tests have been tabulated in Table II. 



*The oleic acid used must be pure. It will not do to leave it exposed to the air for a few months. 

 69 



