Cryptic east-west divergence and molecular diagnostics for two species of silver flies (Diptera: Chamaemyiidae: Leucopis) from North America being evaluated for biological control of hemlock woolly adelgid

Exploring genetic diversity within species of biological control agents can expose previously overlooked beneficial genotypes. This may be the case for two species of silver flies, Leucopis argenticollis and L. piniperda, predators of the hemlock woolly adelgid (Adelges tsugae) in the Pacific Northwest of North America. The same Leucopis species occur in eastern North America, where they feed on other adelgid species, but not on hemlock woolly adelgid, which became a pest in the region after its introduction from Japan earlier this century. We collected DNA sequence data from one mitochondrial and two nuclear genes for 606 Leucopis individuals to examine variation correlated with geographic origin and prey association. Specimens of L. argenticollis and L. piniperda collected from adelgids on hemlock and spruce in the West are phylogenetically divergent from con-specifics collected from adelgids on pine and spruce in the East. These results suggest that within each species, there are distinct lineages that specialize on different adelgid prey on different hosts in western versus eastern North America. The western lineages appear to be strong candidates for enhancing biological control of Japanese hemlock woolly adelgid in the eastern United States, given their widespread occurrence on western hemlock woolly adelgid in the Pacific Northwest, and the absence of these genotypes in the East. We also developed a PCR-RFLP assay based on the mitochondrial COI gene as an inexpensive and reliable way to distinguish the four genetic groups to document establishment and impact following release.