Investigations on Racial Biology Especially in Lepidoptera

Genetic and wild population studies have shown that the two races of Colias chrysotheme are different on a multiple-factor basis, these including physiological differences as well as a color difference. Sterility in the crosses may be largely related to diet differences between the races though evidence is presented to show that the hybrid segregants are less viable than the parental types. A wild population where intercrossing occurs shows about 10% of intermediates - mostly fertile. A dominant autosomal gene for white female color is found in wild populations of both races. Genetic results indicate that it is probably homologous in the two races and is interchangeable between them. The gene may be either lethal or semi-lethal with certain modifiers when homozygous dominant. Within each race the gene is most abundant in the northern populations as compared with the southern. The history of the recent establishment of the orange race in the area east of the Mississippi River is reviewed; the evidence shows that the planting of alfalfa in that area has been the primary factor which has encouraged the extension of range of the butterfly. The causes of genetic alterations in wild populations has been studied by means of the white females. Genetic population changes are described which have been caused by migration, environmental selection, random fluctuations and differential development rate of the genotypes.