Seasonal Abundance, Defoliation, and Parasitism of Japanese Beetle (Coleoptera: Scarabaeidae) in Two Apple Cultivars

The Japanese beetle, Popillia japonica Newman, is an invasive insect to the United States that feeds on turfgrass roots as a larva and the foliage, flowers, and fruit of many major ornamental and agricultural crops, such as apple, as an adult. Despite its generalist feeding behavior, P. japonica shows preferences for certain plant species and cultivars. Classical biological control for P. japonica, including release of Istocheta aldrichi (Mensil), has been pursued in Minnesota. This study was conducted to assess the effects of apple cultivar on season-long abundance of adult P. japonica and their defoliation; and to assess effects of apple cultivar and P. japonica abundance and sex on parasitism of P. japonica by I. aldrichi. Sampling occurred during the summers of 2017 and 2018 on Zestar! and Honeycrisp cultivars in four different apple orchards. Abundance and defoliation of P. japonica was higher on Honeycrisp than Zestar!. Parasitism of P. japonica by I. aldrichi was higher for females than for males. In 2018, the relationship between parasitism of P. japonica and host density varied by cultivar. These findings may help growers determine which apple cultivars should be prioritized for scouting and management efforts and may provide an estimate of potential biological control by I. aldrichi in agricultural areas in the Midwest.