Development of azalea lace bug, Stephanitis pyrioides (Scott), on susceptible and resistant Rhododendron spp. in western Washington

The invasive azalea lace bug, Stephanitis pyrioides (Scott), is a serious pest of Rhododendron species, especially azalea (subgenus Azaleastrum) Introduced into the United States in 1915, its presence was confirmed in Washington State in 2008. Feeding by S. pyrioides decreases plant vitality and reduces the aesthetic qualities of the plant, and plant death can occur in severe infestations. Because S. pyrioides is relatively new to the Pacific Northwest, little is known regarding the susceptibility of Rhododendron species in the region, and S. pyrioides development and voltinism. We quantified susceptibility from 71 different Rhododendron species, varieties, and cultivars over two years by measuring leaf damage. Among subgenera, plants from Azaleastrum were the most susceptible, and plants from Hymenanthes were the most resistant. Among Section, plants from Tsutsusi (evergreen azaleas) were the most susceptible, and plants from Ponticum were the most resistant. We then developed a degree day model of immature development by intensively sampling S. pyrioides life stages 1-2 times per week over two years. We also estimated that S. pyrioides has two full generations and a partial third in the Pacific Northwest  This research extends our understanding of S. pyrioides in a novel area, and serves to optimize management strategies against this invasive species.