Coleomegilla maculata De Geer is an abundant, widely distributed, New World polyphagous lady beetle. High levels of variation at 14 polymorphic allozyme loci were used to examine breeding structure of populations from New England, Iowa, south Texas, and Honduras. Analysis of variance of gene frequencies and F-statistics showed high levels of gene flow within each region and between the Texan and northern United States populations, but negligible rates of gene flow between these and the Honduran populations. Thus, gene flow was largely unrestricted in North American C. maculata.Honduras populations were highly differentiated genetically from the North American populations and shared with North American beetles only 41 of 70 alleles at 14 allozyme loci. Nei's genetic distances within Honduran, Texas, and Iowa-New England samples did not differ significantly from zero, but the intergroup distances were large. Reciprocal crosses within and between Texas and Iowan populations were fertile, but reciprocal crosses between Honduran and North American strains were completely sterile. No consistent morphological differences between North and Central American C. maculata were detected. Backcrosses of male and female hybrids of Iowa and Texas beetles to either parental strain were fertile. The results indicate two sibling species are present, one in North America and another in Honduras.