Abstract

<jats:p> The effect of nine insecticidal compounds upon the rate of heartbeat of the American cockroach was ascertained by their injection into adult male insects at a dosage of 80 μgm. per individual, corresponding to 100 mgm. per kgm. body weight. The chlorinated hydrocarbons DDT, lindane, chlordane, and toxaphene exerted little effect, the maximum response being a slight acceleration. The dinitro compounds DNOC and DNCHP caused an increase in rate, followed by total failure of the heart. Parathion and thiocyanoethyl laurate proved to be slightly stimulatory in the concentrations employed. Rotenone steadily depressed the rate of heartbeat until it stopped. Similar effects were produced by applying the insecticide in a contact spray in benzene-kerosene mixture, although the solvent caused an initial drop in heart rate that was probably associated with temporary narcosis. The heart of decapitated insects showed a gradual decrease in pulsation rate and was less sensitive to the effects of insecticides. </jats:p>