Find out the light moths against the soot-darkened

Q. The peppered moth provides a well-known example of natural selection. The light-coloured form of the moth was predominant in England before the industrial revolution. In the mid-nineteenth century, a dark-coloured form appeared. The difference is formed by a dominant allele of one gene. By about 1900, around 90 percent of the moths around industrial areas were dark coloured, whereas light-coloured moths were still abundant elsewhere. In fact, birds could readily find out the light moths against the soot-darkened background in industrial areas and therefore were eating more light moths. Recently, use of cleaner fuels has greatly reduced soot in the landscape, and dark-coloured moths have been disappearing. Should the two forms of moths be considered separate species?