Genetic differentiation among populations of velvetbean caterpillars (Anti-carsia gemmatalis Hübner) was examined to determine likely migratory pathways taken during invasion of the southeastern United States each summer. Specimens were collected from three sites in the southeastern United States in 1982 and 1983 and three sites in middle America in 1983. Nineteen of 28 enzyme loci surveyed electrophoretically were polymorphic. Single-pair crosses verified a Mendelian mode of inheritance for nine polymorphic loci exhibiting variation in the parents. Eight loci exhibited significant heterogeneity among populations. Populations collected in Louisiana and middle America were identical to each other at all loci but different from populations in South Carolina and Florida. Florida was most distinct. A rare allele analysis supported the divergence of the Florida population. Small genetic distances among populations suggest high levels of gene flow (and migration) within this species relative to other organisms. The pattern of differentiation suggests that southcentral United States populations may originate in Mexico rather than from overwintering populations in southern Florida.
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Pashley et al. (1986) studied this question.