JOURNAL 
OF 
ECONOMIC ENTOMOLOGY 
OFFICIAL ORGAN AMERICAN ASSOCIATION OF ECONOMIC ENTOMOLOGISTS 
Vol. 11 DECEMBER, 1918 No. 6 
OBSERVATIONS ON THE MODE OF ACTION OF CONTACT 
INSECTICIDES 1 
By William Moore, Division of Entomology and Economic Zoology, 
University of Minnesota 
During the present year, certain experiments have been conducted, 
which throw further light on the action of contact insecticides, and 
since it does not appear possible to make a more complete study in the 
near future, the following brief account is given in the hope that it will 
prove of some value to entomologists. 
In a recent paper on essential physical properties of contact insecti¬ 
cides, 2 it was shown that fat solvents, oils and soaps were able to pene¬ 
trate the tracheae of insects by capillarity. It was further noted that 
heavy, practically nonvolatile and nontoxic oils, which had thus pene¬ 
trated the tracheae caused the death of the insects, but that the tissues 
of such insects were not stained by trypan blue (which stains dead 
tissue and not living tissues) until, ten, twenty or more hours had 
elapsed. From these observations, the question arose as to whether 
the insects did not die from the lack of oxygen resulting from the 
closing of the tracheae. Shafer 3 has shown that methylene blue or 
indigo carmine injected into the body of an insect, which is then placed 
in an atmosphere free of oxygen, is reduced to its leuco compound and 
the body of the insect again becomes white or jmllowish white. Upon 
1 Published with the approval of the Director as Paper No. 141, of the Journal 
Series of the Minnesota Agricultural Experiment Station. 
2 Moore, Wm., and Graham, S. A. Physical Properties governing the efficacy of 
Contact Insecticides. Journ. of Agr. Res. Vol. xiii, No. 11, 1918, pp. 523-538. 
3 Shafer, Geo. D. How Contact Insecticides Kill. Mich. Agri. Exp. Sta. Tech. 
Bull, 11-65 p., 1911. 
2 
