On the evidence against the chemical induction of melanism in Lepidoptera

McKenny Hughes (1932) has reported an experiments, carried out at Merton, in which the moth Selenia bilunaria Esper was fed on leaves treated with lead nitrate and manganous sulphate. In the generations following these treatments no instance of a moth showing the melanic recessive mutation, reported by Harrison and Garrett (1926), was recorded. In the discussion contributed by Haldane (McKenny Hughes (1932), p. 400) it is argued that the results are significantly in conflict with the findings of Harrison and Garrett in that these authors recorded 6 melanics out of 142 moths of the generations following treatment, while McKenny Hughes found no melanics among 910 moths. This difference, as Haldane claims, would be highly significant, if the several individuals counted had an independent chance of being melanics, In both lots, however, the moths were in reality closely related, and the chances cannot on any theory be considered independent. The other calculations in Haldane’s discussion are open to the same criticism.