Y54 EXPERIMENT STATION EECOED. 



8-53) deals with the effects of certain gases and insecticides upon the activity 

 and respiration of insects, and the second (pp. 53-64) with some properties of 

 lime-sulphur wash that make it effective in killing scale insects, especially San 

 Jose scale. Abstracts of these have been previously noted (E. S. R., 25, p. 665). 

 The investigations conducted and here reported in detail have been summarized 

 by the author in the following general conclusions : 



"Usually contact insecticides do not depend upon one property or means, 

 alone, for their effectiveness, yet as a rule some one property is chiefly concerned. 

 Alkaline washes, corrosive sublimate solution, and other fluids, which are capable 

 either of dissolving or of precipitating certain constituents of insect tissues, are 

 able to penetrate the chitin of insects into the tissues slowly. The weaker the 

 surface tension of the fluid, apparently, and the thinner the chitin with which 

 it is in contact the more rapid- the penetration. Gases and vapors may penetrate 

 the chitin of insects, especially through the trachefe, into the tissues far more 

 rapidly than liquids. 



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

 kerosene, gasoline, creolin, pyrethrum 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 trachesB 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 rest 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 uncer- 

 tain 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 wMle 

 they are alive. For the most part, these gases are not given oft" 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, gasoline, or similar vapor 

 and no more (at that percentage) is taken up. Then when the insects are ex- 

 posed 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 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 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 continue to give off 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, kero- 

 sene, carbon disulphid and the like, after absorption into the insect body, be- 

 come mainly effective through some tendency their presence exerts to prevent 

 oxygen absorption by the tissues. 



