The comparative toxicity of various contact insecticides to the louse Pediculus humanus (L.) and the bed bug (Cimex lectularius L)

A variety of substances has been tested by laboratory methods as insecticides against the bed-bug and the body-louse. The oil-soluble samples were tested by the Potter tower method which gave the most accurate results. Certain liquids were tested by a simple dipping method, and solids insoluble in mineral oils were tested as aqueous solutions by the dipping method or as dusts.

Various organic thiocyanates were found to show similar relative toxicity to the louse and bug, but the pyrethrins were much more toxic to the latter. D.D.T. was highly toxic to both and Gammexane even more insecticidal, especially to the louse.

In the dipping tests, two types of toxic action were observed: an immediate physicochemical action and a delayed lethal action due to asphyxiation. Refined mineral oils kill lice by the latter method. Among the aqueous preparations, the emulsion of cresols known as Lysol was noteworthy for its ovicidal powers.

Some experiments were made with extracts of delphinium seeds, the insecticidal powers of which were shown to reside in the alkaloids.