Some breeding experiments on the geometrid mothHemerophila abruptaria (Thunb.) and two of its melanic varieties

Summary and conclusions

1. The atmospheric humidity at which these insects are reared does not affect the intensity of wing colour of either the melanics or the types. The lighter form of the melanic which appeared for the first time in the course of the humidity experiment was, from its distribution, obviously not a result of the humidity at which it was reared.

2. The factor for “dark” melanism is a simple Mendelian dominant to type.

3. Two forms of melanic variety have appeared. The “light” form is probably due to a sex-linked factor which modifies the “dark” melanism. In view of the small numbers appearing, and the predominance of the female sex, it seems unlikely that it is inherited without any complications, and it must be some sort of recessive character, as it did not appear in theF ₄ generation, and reappeared inF ₅.

4. A rather high pupal mortality has been noted, and there has been a marked sexual difference, the males being much less viable than the females. The reason for this is obscure, but it may be due to a sex-linked lethal factor.

5. Further analysis of the data gives evidence that there is no difference in viability between the types and the heterozygous melanics, but that the homozygous melanics are less viable than either of the others. This is in direct contradiction to Onslow’s conclusion.