ROLE OF FOLIAR PHENOLICS IN HOST-PLANT RESISTANCE OF MALUS TAXA TO ADULT JAPANESE-BEETLES

Japanese beetles (JB),Popillia japonica Newman, are destructive, highl y polyphagous herbivores that show a general preference for Rosaceous plants. Choice and no-choice feeding assays were conducted to determin e the level of resistance among 10 taxa of Malus spp. Mill. Under no-c hoice conditions, M. baccata (L.) Borkh. 'Jackii', M. x 'Hargozam' Har vest Gold and M. transitoria (Balatin) Schneider 'Schmitcutleaf' Golde n Raindrops were highly resistant, with <2 cm(2) leaf area consumed in 24 hours. M. x 'Radiant' was highly susceptible, with 7.6 cm(2) consu med, and the remaining six cultivars were intermediate, Under choice c onditions, eight tars were resistant with <10% defoliation, M. x 'Red Splendor' was intermediate with 26%, and M. x 'Radiant' was susceptibl e with 73% defoliation. Feeding responses to eight individual phenolic s were tested in artificial diets over a range from 0 to 100 mM. Phlor idzin, phloretin, naringenin, and catechin were sill feeding deterrent s; whereas quercetin and rutin were feeding stimulants. Chlorogenic ac id stimulated feeding at low concentrations and deterred feeding at hi gher concentrations (i.e., a peak response). Kaempferol had no effect. Analysis of endogenous foliar phenolics showed considerable variation in concentrations among taxa. Stepwise multiple regression analysis i dentified phloridzin as the only endogenous phenolic that was signific antly related to resistance under both choice and no-choice feeding co nditions.