Harnessing host plant resistance in Betula spp. to manage Popillia japonica in ornamental landscapes

Popillia japonica (Japanese beetle), an invasive insect pest in North America, can cause extensive damage to more than 300 horticultural plants including birch (Betula spp.) and grapevine (Vitis spp.). While chemical control remains the primary tool to manage Japanese beetle, host plant resistance offers a sustainable alternative. This research utilizes the woody plant collections at the Minnesota Landscape Arboretum to investigate specialized metabolites and physical traits that underlie P. japonica feeding preferences in birch. We conducted field observations and laboratory no-choice and two-choice feeding assays to evaluate resistance mechanisms among selected plant genotypes. In the field, an inverse correlation was observed between P. japonica herbivory and infestations by another insect pest, Agrilus anxius (bronze birch borer). Laboratory assays measured leaf area consumed using digital image analysis. Birch genotype UMNBA#29 consistently experienced less feeding in the field and both lab assays, suggesting potential resistance traits. To assess the role of leaf chemistry, we extracted leaf compounds from UMNBA#29 with water, hexane, and dichloromethane and applied the extracts to susceptible leaves. However, extract treatments showed no consistent effect on feeding, indicating complex interactions of plant chemistry in host selection. Future research will investigate a grapevine mapping population to identify genetic markers associated with resistance, analyze specialized metabolite profiles, and test whether resistance can be induced using jasmonic acid. This study contributes foundational knowledge on host plant resistance and may inform plant breeding and natural insecticide development to support integrated pest management strategies.