Geographic Variation in Adult and LarvalLophocampa maculataHarris 1841

Abstract

The spotted tussock moth, Lophocampa maculata Harris 1841, inhabits a wide band of North America on both sides of the United States/Canadian border from coast to coast and extends southward along the Pacific coast and in the major mountain ranges of the United States. Within this large range, the species exists as several geographic variants characterized by a number of phenotypic differences, most notably last instar larval coloration. Other distinctions include voltinism, with the California coastal variety being uniquely bivoltine, and larval food preference. While considered a generalist feeder on broadleaf trees, some geographic variants show strong preferences for a particular genus of food plant. Over most of its range, L. maculata exists in one of two larval color patterns. Last instars of the Eastern and California Coastal forms are a combination of black and yellow, while the Western Interior form is a combination of orange and black. However, in the Pacific Northwest there is a stable population exhibiting wide variation in larval coloration, with features of the color patterns of both the other two varieties. An additional, and perhaps unique, feature of larval coloration is the rare occurrence of individuals with partial depigmentation for one or two instars, followed by reversion to normal coloration in the last instar and the adult. These individuals are found in all of the geographic populations, although there are small distinctions in coloration that appear to be population-specific. Larval coloration results from three pigments. Exogenous xanthophylls, obtained from the diet produce the yellow color, whereas the endogenous black pigment is eumelanin. The orange pigment is most likely pheomelanin, produced endogenously.