48 JOURXAL OF ECOXO-MIC EXtOMOLOGV [Vol. 4 



sublimate, penetrate the chitin and precipitate proteicl bodies of the 

 tissue cells. 



Furthermore, kerosene, and some of the insecticides commonly 

 known as the miscible oils appear to depend chiefly on some other 

 property still. It has been generally believed that these latter sub- 

 stances enter the spiracles and suffocate the insects by shutting out 

 fresh air from the trachege. By the use of the stain, Sudan III, in 

 kerosene, gasoline, and such fluids, and by the use of Indigo Carmine 

 in emulsions of the miscible oils, it was shown that contact insecti- 

 cides of this type do enter the spiracles and tracheae of plant lice. The 

 same was true also of caterpillars and insects having a protective 

 closing apparatus for the tracheae, if the fluids were applied thoroughly 

 enough. But, while the presence of these bodies in the tracheae might 

 interfere with the passage of air, it appeared that the insecticides must 

 kill in some other way than by merely plugging the tracheae and depriv- 

 ing the insect of oxygen. Insects, which are killed rapidly by kerosene 

 or gasoline, may revive after many hours' confinement in hydrogen, 

 carbon dioxide, or nitrogen. Some species are able to recover after 

 being deprived of oxygen for a much longer period than others. More- 

 over Passalus cornutus, which is quickly killed by gasoline, is able to 

 recover entirely after being submerged for two minutes in pure oleic 

 acid — until all the tracheae leading from the spiracles are filled. The 

 oleic acid is an oily substance which would be as capable of plugging 

 the tracheae as gasoUne or kerosene. 



At 72° to 84° F. it was found that the vapor of the follo-udng sub- 

 stances would affect insects: Gasoline, benzine, kerosene, to-bak-ine, 

 pyro-cresol, pine oil disinfectant, creohn, crel oil, chloro-naphtholium, 

 zenoleum, aniline oil, and creosote. 



The vapors of the more volatile of these liquids at saturation will 

 kill many insects as rapidly as when an abundant supply of the liquid 

 itself is applied. Death, in the case of the vapor, could scarcely be due 

 to a plugging of the spiracles. Small amounts of the vapor or of the 

 liquid of any of these substances act upon insects much as the common 

 anaesthetics, ether and chloroform. Passalus cornutus is a good insect 

 to use in studying the action of these bodies. One can note upon the 

 first application of a small amount of one of these substances, excite- 

 ment and a more rapid heart beat. Under the influence of larger 

 amounts the actions become uncertain and the heart beat irregular; 

 then the insect will become quiet, and the heart-beats slower and 

 slower until they cease entirely and death results. Hydrocyanic acid, 

 hydrogen suphide, and the volatile portions of pyrethrum act in very 

 much the same way. 



It was found that small amounts of kerosene, gasoline, pyrethrum. 



