Phenology of Hemlock Woolly Adelgid (Hemiptera: Adelgidae) in the Central Appalachian Mountains, USA

The ability to predict key phenological stages of insect pests is of prime importance in sampling and management programs. Hemlock woolly adelgid, Adelges tsugae (Annand) (Hemiptera: Adelgidae), is a non-native invasive pest of eastern and Carolina hemlock that is currently expanding its range westward through the central Appalachian region. We conducted intensive sampling of A. tsugae across four sites in West Virginia and western Maryland from March 2013 to May 2014, and developed a degree-day model (minimum temperature threshold of 4 degrees C) to predict the temporal distribution of progrediens eggs, progrediens egg hatch, newly hatched sistens, and settled first-instar sistens. We then linked degree-day predictions to recent weather data collected from our study region from 2012 to 2016 to provide a range of calendar days over which these key phenological events occur. The initial occurrence of progrediens eggs and progrediens egg hatch is predicted to occur at 209 (mean date of 19 April) and 346 (mean date of 8 May) degree days, respectively. The initial occurrence of newly hatched sistens and settled first-instar sistens is predicted to occur at 852 (mean date of 19 June) and 1010 (mean date of 30 June) degree days, respectively. Because our study region represents a region in which A. tsugae continues to spread, this information should be useful in optimizing sampling programs and the timing of control tactics in the central Appalachian region.