Hemlock woolly adelgid, Adelges tsugae Annand, is a destructive introduced pest of hemlock trees in eastern North America, and management has focused on the use of natural enemies through classical biological control. Two species of chamaemyiid flies, Leucopis argenticollis Zetterstedt and Leucopis atrifacies (Aldrich) have been collected previously from western hemlock trees, Tsuga heterophylla (Raf.) Sargent, infested with A. tsugae in the Pacific Northwest. Leucopis spp. found associated with A. tsugae in the Pacific Northwest are known to be important predators of Adelgidae. Additionally, biological control programs for other adelgid species have employed chamaemyiid predators in the past with varying degrees of success, indicating that Leucopis spp. are good candidates for biological control of A. tsugae in eastern North America.
This study was conducted to determine the degree of host specificity of the Leucopis spp. by evaluating prey suitability and host acceptance in no- choice tests using four adelgid species. While collecting immature Leucopis spp. to use in these tests, we identified a third species, Leucopis piniperda Malloch, associated with A. tsugae in Oregon and Washington. Leucopis spp. survival was highest on A. tsugae, but they were able to complete development on all four adelgid species. These results suggest that Leucopis spp. may have a conservative host range within the Adelgidae, but may not be specific to A. tsugae. Additionally, fourteen western hemlock trees infested with A. tsugae in Oregon and Washington were sampled over a period of 14 months to evaluate the seasonal abundance and synchrony of Leucopis spp. with A. tsugae in the field. Leucopis spp. larvae were collected year-round on branches infested with A. tsugae. There was a positive correlation between Leucopis spp. and A. tsugae abundance. Peak abundance of Leucopis spp. coincided with the presence of both progrediens and sistens eggs of A. tsugae in the field.