VOLATILE COMPOUNDS FROM CRABAPPLE (MALUS SPP) CULTIVARS DIFFERING IN SUSCEPTIBILITY TO THE JAPANESE-BEETLE (POPILLIA-JAPONICA NEWMAN)

The volatile compounds emitted by leaves of four crabapple cultivars s usceptible to damage by Japanese beetles and four relatively resistant cultivars were examined. Twelve compounds, mostly terpene hydrocarbon s, were identified from intact leaves. The terpenes (E)-beta-ocimene, caryophyllene, germacrene D and (E,E)-alpha-farnesene occurred in sign ificantly higher levels in susceptible cultivars, whereas resistant cu ltivars produced greater amounts of (E)-4,8-dimethyl 1,3,7-nonatriene and linalool. The relative attractiveness of the cultivars as determin ed in a pitfall bioassay, however, was not related to their susceptibi lity to the Japanese beetle as previously determined by defoliation su stained in the field. The attractiveness of individual cultivars was f ound to be positively correlated with linalool as a percent of the tot al volatile blend emitted by leaves. This study and previous work sugg est that variation in susceptibility of crabapple cultivars to defolia tion by Japanese beetles is not due to the attractiveness of the indiv idual cultivars but rather to nonvolatile components of susceptibility and/or resistance. A scenario for host location by the Japanese beetl e is presented.