Japanese beetle (Popillia japonica) varietal preference in Minnesota wine grapes

Japanese beetle, (Popillia japonica), is a highly polyphagous, invasive species, first recorded in Minnesota in the late 1960’s. Historically, research on this pest in the Midwest U.S. focused primarily on ornamental and turf crops, with little effort focused on adult feeding and subsequent damage to fruit crops. Due to a recent expansion of beetle populations in Minnesota, growers have observed a substantial increase in defoliation on several fruit crops, which has led to increased concerns regarding the impact of beetle feeding and increased insecticide use. Studies were conducted in the summer of 2020 to determine varietal preference in wine grapes. Six varieties, reflecting popular Minnesota cold-hardy wine grapes, with 3 replications each, were examined for adult feeding damage and population density. Data collection included random, 1-m row sampling of adult beetles per sample date, as well as leaf samples to estimate percentage defoliation. Leaf samples were transported to the lab to estimate defoliation levels using the Leafbyte App. An accompanying laboratory study was conducted using three varieties, Edelweiss, Itasca, and Frontenac, to conduct both choice and no choice tests. Results from these studies demonstrate clear, consistent preferences across the varieties screened. Differences in beetle infestation and defoliation levels suggest that variety selection may play an important role in developing integrated pest management (IPM) programs to manage Japanese beetle in Midwest wine grapes.