The invasive azalea lace bug, Stephanitis pyrioides (Scott), is one of the most damaging insect pests of the genus Rhododendron, especially azaleas. Feeding by nymphs and adults reduces the aesthetic value of infested plants. Rhododendron spp. (L.) and cultivars are a major component of public and private landscapes in the Pacific Northwest, as well as other parts of the U.S.. Variability in the susceptibility of Rhododendron to S. pyrioides has been previously examined but generally on a limited number of Rhododendron species and cultivars. We measured the susceptibility of 71 Rhododendron species, varieties, and cultivars over two years, selecting plants across the phylogenetic tree of Rhododendron, and quantified the proportion of leaf damage caused by S. pyrioides. We observed that trichome presence did not predict S. pyrioides damage. Plants from the subgenus Azaleastrum were the significantly most susceptible subgenus, and all sampled plants from this subgenus had measurable damage. In contrast, plants from the subgenus Hymenanthes were the significantly least susceptible, and most Hymenanthes plants had no measurable damage. This study provides a guideline for using host plant resistance to S. pyrioides in plant selection, and emphasizes the potential for S. pyrioides management if susceptible azaleas are to be used in the landscape. Species used in this study: Azalea lace bug, Stephanitis pyrioides, Rhododendron spp.

The invasive azalea lace bug, Stephanitis pyrioides (Scott) (Tingidae: Hemiptera), is an important pest of Rhododendron (L.) (Ericales: Ericaceae). Feeding by nymphs and adults removes chlorophyll, reduces rates of photosynthesis and transpiration, and causes leaf stippling, which reduces the aesthetic value of infested plants. Rhododendron spp. are a major component of landscapes in the Pacific Northwest. Previous studies on the seasonality of S. pyrioides in North America are largely from the southeastern United States, which could have limited applicability in the Pacific Northwest. To quantify S. pyrioides seasonality in western Washington, we sampled ~200 leaves from 18 Rhododendron plants 1–2 times per wk from April to October over 2 yr, and microscopically counted the number of eggs, early instars, late instars, and adults. We developed a degree-day model for first generation S. pyrioides, which we used to estimate that S. pyrioides undergoes two full and a partial third generation in western Washington. Our model estimates 5 and 50% early instar occurrence, after hatching from overwintering eggs, at 69 and 171 accumulated degree-days from 1 January, respectively, when using a base threshold of 10.2°, which can be used to optimize the timing of management decisions. We also observed faster development and adult emergence when S. pyrioides nymphs feed on susceptible host plants relative to more resistant host plants, which may influence the timing of management decisions and potentially increase the probability of a full third generation. This research enhances our knowledge of an emerging invasive species in the Pacific Northwest.

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