As a basis for future investigations on the development and the nature of resistance against insecticides, the regression lines for the toxicity of γ-hexachlorocyclohexane to D. melanogaster were estimated by means of
1. A contact method, in which the insects (adults) were exposed to a treated surface.
2. A skin-application method, in which measured doses of an acetone solution of the poison were used.
3. An injection method in which adults were injected with known doses of an emulsion containing the insecticide.
The reproducibility of the results obtained with the above methods is briefly discussed. It was found that in the case of the skin-application and injection methods the regression line did not deviate significantly from linearity. The same was true for the contact method if the results obtained with the smaller doses were not taken into consideration.