Bioassays for measuring the resistance of different apple cultivars to thedevelopment of leafrollers (Lepidoptera : Tortricidae)

Bioassays are described for measuring the resistance of different apple (Ma lus domestics Borkh.) cultivars to the development of three leafroller spec ies, Planotortrix octo Dugdale, Epiphyas postvittana (Walker), and Ctenopse ustis obliquana (Walker). Neonate larvae were released onto individual leav es of each cultivar in square plastic petri dishes kept at 20 degrees C. Th e development rate, size of larvae, and survival, and the weight and sex of pupae were recorded and compared between cultivars. No C. obliquana larvae developed fully on 'Granny Smith', 'Royal Gala', and 'Prima', whereas 90-1 00% pupated on 'Liberty' and 'Red Dougherty'. P. octo larvae had high survi val rates (80-100%) on all cultivars but pupal weights were highest on 'Red Delicious'. E. postvittana larvae also survived well (80-100%) on all cult ivars but development rates differed between cultivars, in part related to significant differences in the proportion completing six instars. The bioas say method gave repeatable results and successfully identified antibiosis a nd susceptibility to leafroller development in apple cultivars.