Abundance of Japanese beetle adults and its parasitoid Istocheta aldrichi in a Quebec commercial vineyard

Japanese beetles ( Popillia japonica Newman 1841 – Coleoptera: Scarabaeidae) were detected in early 2000’s at L’Orpailleur, a commercial vineyard located in Dunham, Quebec. Canada. As their levels of damage increased significantly since 2014, a research project was conducted to document the abundance of Japanese beetle adults on foliage of vines and its parasite, the winsome fly Istocheta aldrichi (Mesnil) (Diptera: Tachinidae). From 2019 to 2023, the abundance of Japanese beetle adults was visually assessed in plots (3 × 24 m of grapevine rows) on foliage of each Vidal and Seyval Blanc cultivars. The abundance of Japanese beetle adults with at least one Istocheta aldrichi egg on their pronotum was also visually assessed. From 2019 to 2023, cages positioned near the vineyard allowed to overwinter I. aldrichi pupae to determine the first date of emergence of I. aldrichi adults. Cumulative day-degrees (>10 °C, starting April 1 st ) were used to report the events related to P. japonica adults, I. aldrichi , and the date of occurrence of phenological stages of grapevines (cultivar Seyval Blanc). In the monitored plots, the seasonal total number of P. japonica adults counted on Seyval Blanc foliage varied from 1955 in 2019 to 513 in 2023, while it varied from 2151 in 2019 to 496 in 2023 on Vidal foliage. From 2019 to 2023, during the period of oviposition of I. aldrichi , the seasonal average % of P. japonica adults showing at least one I. aldrichi egg on its pronotum varied from 7.6 in 2020 to 41.7% in 2023 on the cultivar Seyval Blanc, while it varied from 10.6 in 2020 to 35.5% in 2023 on the cultivar Vidal. Having discussed the agronomic context and factors involved at l’Orpailleur, we conclude that I. aldrichi had a major impact on P. japonica populations, thus providing a non-insecticidal and sustainable tactic to manage this insect.