2006 Annual Report 4d.Progress report. This report serves to document research conducted under a reimbursable agreement between ARS and the U.S. Forest Service. This research was carried out in collaboration with U.S. Forest Service Center for Forest Health Research partners and with assistance from the U.S. National Arboretum Gardens Unit and Germplasm Units. Additional details can be found in the report for the parent project 1230-21000-043-00D Genetic Improvement of Landscape Trees for Superior Pest Resistance. Hemlock woolly adelgid is a devastating imported pest of native eastern hemlock which is an important forest and landscape tree. Our approach is to create and evaluate hybrids between the susceptible native American species and resistant Asian germplasm, in particular, T. chinensis. Interspecific hemlock hybrids and species were field inoculated with hemlock woolly adelgid in spring 2006 and data is being collected on infestation and reproduction of the adelgids through spring 2007 as is data on size, cone-bearing and fertility of hybrids. Propagation experiments of interspecific Tsuga hybrids and species were initiated in February and July 2007, and rooting evaluation of over 2000 cuttings has begun. A replicated field planting of documented wild collected Tsuga chinensis germplasm is completed.