mtDNA-based identification of Lucilia cuprina (Wiedemann) and Lucilia sericata (Meigen) (Diptera: Calliphoridae) in the continental United States

Abstract

Existing data suggest that the forensically important dipteran species Lucilia cuprina (Wiedemann) and Lucilia sericata (Meigen) may be particularly difficult to discriminate using DNA sequence data. L. cuprina is paraphyletic with respect to L. sericata in mtDNA phylogenies, with some L. cuprina having mtDNA haplotypes that are very similar to those of L. sericata. We examine this problem by providing the first DNA data for L. cuprina from North America, including portions of both the mitochondrial COI gene and the nuclear 28S rRNA gene. With the new data, L. cuprina remains monophyletic for 28S but paraphyletic with respect to L. sericata for COI. However, we find that all flies that are identified as L. cuprina by morphology and have L. sericata-like mtDNA form a distinctly monophyletic mtDNA clade. This clade may possibly have originated by hybridization between L. cuprina and L. sericata, but its wide geographic distribution strongly suggests a singular origin as opposed to repeated incidents of hybridization. The phylogenetic results strongly support the hypothesis that L. cuprina and L. sericata can be discriminated using mtDNA sequence data. We find that a fragment of COI spanning approximately 1200 base pairs is sufficient to discriminate between the two species with greater than 95% bootstrap support.