Potential feeding deterrents of Adelges tsugae found in biological control flies

The invasive hemlock woolly adelgid, Adelges tsugae (HWA, Hemiptera: Adelgidae), is a detrimental pest to native eastern and Carolina hemlocks. In the last 2 decades, biological control utilizing two species of Laricobius beetles (Coleoptera: Derodontidae) has been of focus in the widespread effort to control HWA. Recently, two species of silver flies, native to the Pacific Northwest, Leucotaraxis argenticollis Zetterstedt and Leucotaraxis piniperda Malloch (Diptera: Chamaemyiidae), are being investigated as additional biological control agents. Releasing these two silver fly species in the eastern United States has yet to result in the establishment of these predators. During laboratory studies, Leucotaraxis larvae excreted a black substance in response to being disturbed, which contained anthraquinones previously detected in HWA. Previous research on Laricobius spp. found that the beetles likely sequestered these compounds from HWA. These compounds are feeding deterrents in other insect species. Leucotaraxis argenticollis life stages, their excrement, and honeydew produced by HWA were collected and analyzed by gas chromatography-mass spectrometry. Results showed that these anthraquinones were detected in various life stages of Le. argenticollis immatures and adults that fed on HWA. They were not detected in Le. argenticollis adults that were only fed artificial diet and water, indicating that Le. argenticollis sequesters the anthraquinones from HWA and may transmit the compounds to their eggs.