Development of Insect-killing Fungi for Management of Hemlock Woolly Adelgid (2005)

Fungal isolates showing activity against HWA in laboratory trials were evaluated in a variety of forest trails during spring and fall of 2001-2003 to select the most virulent fungal isolates and determine the best timing and concentration for fungal applications. Fungi were also assayed against Pseudoscymnus tsugae Sasaji and McClure, a predator being developed for HWA management, to evaluate the compatibility of these biological strategies. We found that fall applications were optimal for targeting HWA and resulted in measurable reductions in HWA survival. In laboratory trials there was little or no effect of fungi on survival of P. tsugae and, when examined under forest conditions, fungi having activity against HWA did not reduce P. tsugae survival. The reductions of HWA populations obtained with fungi and fungal compatibility with P. tsugae demonstrates the promise of fungi as a component in the integrated management of HWA. Future research is needed to develop novel formulations for delivery by ULV application, determine spore persistence and dispersal, and expand evaluation of non-target effects. INTRODUCTION Development of biological strategies for management of hemlock woolly adelgid (HWA) is an immediate priority because of environmental and economic considerations limiting use of insecticides. The potential of insect-killing fungi for HWA suppression is highlighted by the observed impact of Entomophaga maimaiga on gypsy moth populations in North America. Fungal isolates showing activity in laboratory trials have now been tested against under field conditions. Compatibility among different biological strategies is imperative. Therefore, our fungi were also assayed against Pseudoscymnus tsugae, a predator being developed for HWA management. Detailed results and general findings are presented. MATERIALS AND METHODS A wide variety of field trails were conducted in the spring and fall of 2001-2003 to select the most virulent fungal isolates and determine the best timing and concentration for fungal applications. Trials were conducted at Mt. Tom Reservation, Holyoke, MA. Fungi were applied to 1m HWA infested branches using hand-held and ULV sprayers (5-6 branches/trt). Both conidia and blastospores were tested at concentrations from 5 x 107 to 2 X 108 spores/ml as either single or multiple applications. Both non-treated and formulation blank treated controls were used. Horticultural oil (0.1%) was used as a positive control. Survival and density of HWA were examined 3-4 weeks post application. Only results from fall population studies are reported. Fungi were tested in both the laboratory and field against P. tsugae obtained from the Alampi Beneficial Insect Lab, Trenton, NJ, only field trials are described here. Beetles were assayed in mesh bags (20/cage with 5 replicates/trt) on intact hemlock branches infested with HWA. Fungi were applied at 1/108 spores/ml using a hand-held sprayer. Branches were excised after 12 days and the survival of P. tsugae was determined. All data was analyzed in SAS using GLM and appropriate models (alpha=0.05). Development of Insect-Killing Fungi for Management of Hemlock Woolly Adelgid Scott D. Costa, Margaret Skinner, Svetlana Gouli, Michael Brownbridge, Vladimir Gouli, William Reid and Bruce L. Parker Entomology Research laboratory, Department of Plant and Soil Science, University of Vermont, Burlington, VT