The invasive azalea lace bug, Stephanitis pyrioides (Scott), is one of the most serious 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. 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. To examine the role of evolutionary history on host plant susceptibility, we analyzed damage in comparison with trichrome presence, as well as subgenera and section of selected Rhododendron plants. We observed that trichome presence did not predict levels of S. pyrioides damage. However, host 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 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.
