Discovery of three woolly apple aphid Eriosoma lanigerum (Hemiptera: Aphididae) biotypes in Australia: the role of antixenosis and antibiosis in apple tree resistance

The woolly apple aphid (WAA), Eriosoma lanigerum Hausmann, is a worldwide pest of apple orchards that has become widespread in apple-growing regions of Australia. Several WAA populations that are geographically distant may have evolved into biotypes having different fitness (e. g. fecundity) in similar biotic and abiotic conditions. In this study, we investigated the performance of four different lines of WAA (designated as ALB, STA, BAT and YAR) originating from four locations in Victoria and New South Wales (Australia). Nymph establishment, nymph development to adult, nymph developmental time, female fecundity and adult weight of apterous virginoparae on apple trees (cv Granny Smith) were monitored under glasshouse conditions. Results showed that at least three lines examined here differ significantly in one or more performance parameters. Nymphs of the STA lineage showed a significantly higher establishment success after 7 days (64.3%) compared with lines BAT (53.1%) and YAR (43.6%). Nymph development to adulthood followed a similar trend. The average fecundity/female/7 days of the ALB lineage (19.7 +/- 1.6 nymphs) was the lowest and significantly reduced relative to all other lines (from 36.6 to 40.5 nymphs). These results demonstrate the existence of at least three different biotypes in Australia. Antibiosis and antixenosis, respectively, could explain lower aphid establishment and lower female fecundity once settled. The characterisation of different WAA biotypes could have important implications for WAA management, and further studies should evaluate the overall diversity of biotypes, their geographical distribution and their growth characteristics to fully optimise pest control strategies.