During the past four decades, several species of aphidophagous Coccinellidae became established in North America, including Coccinella septempunctata, Harmonia axyridis, Hippodamia variegata, and Propylea quatuordecimpunctata. After their
establishment, unknown circumstances favoured a rapid increase in population densities and distribution of H. axyridis and C. septempunctata at localities hundreds and thousands of kilometers from their release sites. Propylea quatuordecimpunctata and Hippodamia
variegata have spread more slowly after becoming established in northeastern North America. Comparative studies based
upon allozyme variation in these four introduced species and in six native North American species of ladybird beetles revealed no
significant differences in genetic diversities. Genetic variation, assessed by allelic diversity and heterozygosity, was uncorrelated
with the establishment and spread of these predatory species in North America. All ladybirds studied show a remarkable degree of
dispersion with little detectable population subdivision.