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We present data from 34 allozyme loci to test whether the Karner Blue butterfly is specifically differentiated from the Melissa Blue. Furthermore, as the Karner Blue is an endangered organism of low vagility that occurs predominantly in small, widely separated populations, we investigated (i) whether the Karner Blue is depauperate in genetic variation and (ii) whether gene flow between sampled populations is unusually low. Genetic identities between New York and Wisconsin populations of the Karner Blue and a sample of Melissa Blue from Minnesota are all statistically indistinguishable. Neither genetic identity data nor application of the phylogenetic species concept support formal recognition of the Karner Blue as a species separate from the Melissa Blue. Nonetheless, the data indicate that gene flow among the samples was very low compared with that among populations of other Lepidoptera. Heterozygosity estimates for all three samples were comparable to data for other Lepidoptera and indicate that the Karner Blue populations surveyed are not under immediate threat of extirpation due to loss of genetic diversity. Although the available data are limited, if the Karner Blue is to be managed as an evolutionarily significant unit, then the eastern and western populations should probably be treated independently and each should receive high conservation priority.

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