The wikipage en.wikipedia.org/wiki/Peppered_moth has more: the different moth colours are called forms and distinguished from sub-species by f., e.g. Biston betularia f. carbonaria
. . individuals of each morph interbreed and produce fertile offspring with individuals of all other morphs; hence there is only one peppered moth species.
By contrast, different subspecies of the same species can theoretically interbreed with one another and will produce fully fertile and healthy offspring but in practice do not, as they live in different regions or reproduce in different seasons. Full-fledged species are either unable to produce fertile and healthy offspring, or do not recognize each other's courtship signals, or both . .
European breeding experiments have shown that in Biston betularia betularia, the allele for melanism producing morpha carbonaria is controlled by a single locus. The melanic allele is dominant to the non-melanic allele . .
These pages are not linked and were evidently created independently.