Aestivation studies and the effect of imidacloprid on the subterranean life cycle of Laricobius spp., biological control agents for the hemlock woolly adelgid

Monday, November 14, 2022

10:30 AM – 10:42 AM PT

Location: Vancouver Convention Centre, Meeting Room 217/218/219

Presenting Author(s)

Ashleigh P. Hillen

Masters Student
Virginia Polytechnic Institute and State University
Blacksburg, Virginia

Co-Author(s)

Jeremiah R. Foley, IV

Post Doc
USDA-ARS
Fort Lauderdale, Florida
AG

Aaron D. Gross

Assistant Professor
Virginia Polytechnic Institute and State University
Blacksburg, Virginia
SH

Sheldon S. Hilaire

Associate Research Scientist
PPD Laboratories
Richmond, Virginia
AM

Albert E. Mayfield

Research Entomologist
USDA-Forest Service
Asheville, North Carolina
Mary K. Salcedo

Biological and Environmental Engineering
Cornell University
Blacksburg, Virginia
JS

Jake J. Socha

Professor
Virginia Polytechnic Institute and State University
Blacksburg, Virginia
KX

Kang Xia

Professor
Virginia Polytechnic Institute and State University
Blacksburg, Virginia
SS

Scott S. Salom

Professor
Virginia Polytechnic Institute and State University
Blacksburg, Virginia

The invasive hemlock woolly adelgid (HWA) Adelges tsugae (Annand) (Hemiptera: Adelgidae) has spread throughout most of the range of eastern hemlocks, Tsuga canandensis (L.) and the entire range of Carolina hemlocks, Tsuga caroliniana (Engelman) causing devastation of this foundational tree species. HWA managers often implement an integrated pest management (IPM) strategy combining chemical, silvicultural, and biological control tactics. Laricobius spp. (Coleoptera: Derodontidae) have been used as biological control agents of HWA since 2003, occupying a subterranean and arboreal life phase synchronous with HWA. Within forests under IPM tactics, there is potential for Laricobius spp. to land on insecticide-treated trees and settle below the tree’s drip line for the subterranean phase of its lifecycle. Imidacloprid is the most widely used insecticide for HWA management. It has been shown persist in the soil for up to four years post-application, and along with metabolites, has been found to negatively impact soil microarthropods. During the subterranean portion of their lifecycle (May-October), Laricobius adults undergo aestival diapause. There is limited knowledge of this portion of their life cycle, specifically the depth at which they occupy and how imidacloprid and its metabolites impact aestivation. Field investigations took place to assess the impact of chemical treatments on the subterranean life phase of Laricobius spp. by quantifying imidacloprid and metabolite soil concentrations and correlating that to percent adult emergence from the soil in the fall. Utilizing 3D X-Ray microscopy, Laricobius spp. burrowing depth was studied to further investigate the interaction of imidacloprid and Laricobius spp. during their aestivation.