EXPERIMENT STATION BULLETINS. 435 



HOW CONTACT INSECTICIDES KILL. 



Technical Bulletin No. 21. 



III. Relating evidence, further, of certain properties of carbon disul- 

 phide, gasoline, and a few other fluids, as well as temperature and some 

 dry powdered contact insecticides, by means of which the insecticidal 

 action of these agents is accomplished after their absorption into the 

 insect tissues, or after mere application; — also brief suggestions for 

 possible practice, by George D. Shafer. 



INTRODUCTORY STATEMENTS, 

 (a) FORMER EVIDENCE. 



In a former paper on the subject, "How Contact Insecticides Kill*," 

 it has been shown that many gaseous or volatile contact insecticides 

 mainly become effective after being taken up by the insect tissues. 

 Certain color tests and actual volume measurements demonstrated that 

 gaseous insecticides, (such as HoS, HCN and NH^) and the vapor of 

 carbon disulphide, as well as that from many volatile oils (e. g. kerosene, 

 gasoline, benzine, turpentine) are absorbed by the tissues of insects. Much 

 evidence was pointed out which indicated that vapors of gasoline, carbon 

 disulphide and the like, after absorption, accomplish their effect upon 

 insects through some tendency their presence exerts to prevent oxygen 

 assimilation in the tissues. 



If the vapors of the insecticides mentioned do interfere with oxygen 

 assimilation, upon what do they act in the tissues to bring about that 

 condition ? 



At the time the former bulletin was written nothing had been done 

 upon this latter phase of the problem. It is with facts that seem to re- 

 late to this phase of the question that the present bulletin has to do. 

 Careful examination was made of the organs of treated insects and many 

 histological studies were made. When an insecticide, such as gasoline, 

 was present in abundance, it was found that after several hours the 

 fatty tissues went more or less into solution. Insects were crushed and 

 an attempt was made to detect changes which carbon disulphide, kero- 

 sene, gasoline and the like might have upon the tissue-pulp. It was 

 easy here also to notice the solvent action of gasoline, kerosene and carbon 

 disulphide upon the fats and fat-like substances in the pulp. The action 

 of carbon disulphide upon protein in the pulp could also be seen. The 

 concentrated vapor of carbon disulphide would, in time, coagulate and 

 whiten certain proteins. Egg-albumen readily shows this action of car- 

 bon disulphide vapor, after a few hours confinement with air saturated 

 at about 68° to 70° F. with that vapor. Studied in this way, however, 

 using only such amounts of the agents in question as were necessary to 



♦Parts I and II, Tech. Bulletin No. 11, Mich. Agr. College Exp. Station. 



