Resistance of Flowering Crabapple Cultivars to Defoliation by the Japanese Beetle (Coleoptera: Scarabaeidae)

Abstract

Flowering crabapples, Malus spp., are important small landscape trees in much of the United States and southern Canada. We evaluated 42 cultivars of Malus spp. for resistance to defoliation by Japanese beetles, Popillia japonica Newman, for 2 growing seasons and found marked and consistent variation in resistance. Defoliation caused by beetles ranged from 100 to <10% among cultivars at the same site. ‘Radiant’, ‘Red Splendor’, ‘Royalty’, ‘Liset’, ‘Ruby Luster’, and others were severely damaged, whereas M. baccata ‘Jackii’, ‘Harvest Gold’, and ‘Jewel berry’ were highly resistant in both years. Red - and purple-leaved cultivars, and those with reddish young leaves that mature to green, were generally fed upon more heavily than were cultivars with wholly green leaves. The rank order of cultivars in no-choice leaf disk assays was correlated with damage levels in the field. Longevity and fecundity of females were highest for beetles fed foliage from preferred cultivars. Possible mechanisms of resistance to P. japonica, and the relationship of our results to earlier studies of resistance of Malus spp. to diseases and other insect pests are discussed.