The small early "spring form" of the eastern tiger swallowtail butterfly, Papilio glaucus has been described from Massachusetts and Illinois in the north, southward all the way into North Carolina. The wing size, shape, patterns, and color all resemble the northern subspecies, P.g. canadensis. The possibility was explored that the "spring form" could in fact be a reflection of genetic introgression from the northern subspecies into P.g. glaucus populations with laboratory hybrid and back cross studies between P.g. glaucus and P.g. canadensis under controlled environments on common foodplants. In addition, morphometric multivariate discriminant analyses of 18 wing characters showed that a P.g. canadensis genetic component to the 'spring' form could account for much of the wing pattern, size, and shape. Some environmental effects manifested during the diapause stage could also be involved in wing phenotype determination. Both genetic and environmental influences are likely to be involved in the explanation of the "spring form" Papilio glaucus throughout eastern North America.
Scriber, J. Mark
"Interaction of Introgression From Papilio Glaucus Canadensis and Diapause in Producing "Spring Form" Eastern Tiger Swallowtail Butterflies, P. Glaucus (Lepidoptera: Palilionidae),"
The Great Lakes Entomologist, vol 23
Available at: https://scholar.valpo.edu/tgle/vol23/iss3/2