Screening for Resistance in Apple Cultivars to Lightbrown Apple Moth, Epiphyas Postvittana, and Greenheaded Leafroller, Planotortrix Octo, and Its Relationship to Field Damage

The mature leaves of 38 apple ( Malus domestica Borkh.) ( Rosaceae) cultivars were screened for resistance to laboratory colonies of Epiphyas postvittana ( Walker) and Planotortrix octo Dugdale ( Lepidoptera: Tortricidae) by measuring larval survival and development rate, and pupal weight, in no-choice laboratory bioassays in early summer. There were few cultivar effects on larval mortality but Nevis 1, A40R04T119, and 'Sir Prize' reduced survival of E. postvittana. Effects on development time and weight were correlated, and were integrated into a single measure of resistance R c. R c varied greatly between cultivars for both leafroller species, and identified 15 and 11 cultivars with partial resistance to E. postvittana and P. octo, respectively. A further experiment with three of the cultivars in midsummer, using the laboratory colonies in comparison with new colonies ( from field collected larvae), produced similar results for E. postvittana, but there was no survival of new colony P. octo larvae on two cultivars. These results for P. octo are consistent with other recent research showing extreme cultivar resistance and critical colony and seasonal influences. A series of 4-year field trials with the 38 cultivars showed poor correlation between laboratory and field resistance for the dominant leafroller species in the field, E. postvittana. The combined data, however, identified 'Red Dougherty', 'Sir Prize', and A40R04T119 as potentially useful in breeding for resistance to this species. The implications of these findings for integrated pest management (IPM) programmes and for the breeding of leafroller-resistant apple cultivars are discussed.