Feeding and oviposition studies of Leucotaraxis spp. (Diptera: Chamaemyiidae), predators of hemlock woolly adelgid (Hemiptera: Adelgidae), in relation to increasing prey densities

Two species of Leucotaraxis Gaimari & Havill (Diptera: Chamaemyiidae), predators of hemlock woolly adelgid, Adelges tsugae Annand (HWA, Hemiptera: Adelgidae) on western hemlock, Tsuga heterophylla (Raf.) Sarg. (Pinales: Pinaceae), in western North America, are currently being investigated as potential biological control agents for HWA in eastern North America. To evaluate their potential for biological control of HWA on eastern hemlock, Tsuga canadensis (L.) Carrière (Pinales: Pinaceae), we conducted laboratory studies to assess their feeding and oviposition responses to different HWA densities. Leucotaraxis argenticollis Zetterstedt was only assessed on the first of 2 generations of HWA, while Leucotaraxis piniperda Malloch was assessed on both generations of HWA, as their phenology in the eastern United States is unknown. Increasing prey densities of HWA ovisacs were used to assess the oviposition of both species of silver flies. Leucotaraxis argenticollis significantly increased their oviposition in response to an increase in HWA densities on the sistens ovisacs containing progrediens eggs, while Le. piniperda showed no significant response for either generation of HWA. Overall, there was no difference in oviposition rates between species; however, Le. argenticollis laid their eggs more frequently on or under the ovisac than Le. piniperda. Increasing prey densities of HWA ovisacs were utilized to assess the feeding response of Le. argenticollis larval feeding. Leucotaraxis argenticollis significantly increased their feeding in response to increased prey densities. These laboratory studies suggest Le. argenticollis has potential as a biological control agent, and both species warrant further investigation.