Bioassays for measuring ovipositional and larval preferences of leafrollers (Lepidoptera : Tortricidae) for different cultivars of apple

Bioassays are described for measuring the ovipositional and larval preferen ces of three leafroller species, Planotortrix octo, Epiphyas post vittana, and Ctenopseustis obliquana, for different apple (Malus domestica) cultivar s. In four-cultivar choice tests, mated female moths were offered terminal shoots in a large screen cage; first instar larvae selected terminal leaves in a smaller test arena. There were high levels of oviposition and settlem ent on all cultivars which agreed with field evidence of their susceptibili ty. However, there was overall higher oviposition of the three leafroller s pecies (combined) on 'Royal Gala' compared to 'Jonafree', and for E. postvi ttana, higher oviposition on 'Liberty' than 'Jonafree'. These cultivar pref erences were also expressed in the responses of the first instar larvae of the respective species. The preference of E. postvittana larvae for 'Libert y' and 'Royal Gala' rather than 'Fiesta', and the preference of P. octo lar vae for 'Liberty' rather than 'Jonafree', were not matched by adult oviposi tion behaviour of the species. C. obliquana showed no significant cultivar preferences but the acceptance ranking of the cultivars was the same in bot h the oviposition and larval tests. The bioassays are considered suitable f or testing of leafroller oviposition and larval preferences using a wider g enetic pool of apple cultivars in parallel with measurements of leafroller colonisation in the field.