Investigating woolly apple aphid (Eriosoma lanigerum) (Hausmann, 1802) migration dynamics and parameters in a Fuji apple tree orchard during the 2023 and 2024 spring seasons

Abstract

Migration data obtained by applying sticky bands on individual trees for two years were pooled into replicates to strengthen statistical analyses and to derive N1 population migration parameters. Destructive shoot sampling was omitted in this study and replaced by non-destructive measurements of shoot occupation, expressed as the percentage of occupied internodes. Although this approach reduced detailed information on colony size, it preserved canopy integrity and provided a sufficiently precise and representative assessment at plant and plot level. Woolly apple aphid (WAA) upward migration intensity alone does not determine canopy infestation by Eriosoma lanigerum (Hausmann, 1802)(Hemiptera: Aphididae). Downward counter-migration, before and during the migration peak, must be considered to estimate true canopy infestation pressure. Results indicate that changes in migration direction after the migration peak cannot be explained solely by temperature. Downward migration of older nymphal instars was confirmed using adhesive bands. Data possibly indicates a relationship between these stages on trunks and the subsequent flight activity of Aphelinus mali (Haldemann, 1851) (Hymenoptera: Aphelinidae). Ongoing studies are examining this phenomenon in other apple-growing regions of South Tyrol.