LEAF SURFACE-COMPOUNDS AND OVIPOSITION PREFERENCE OF TURNIP ROOT FLY DELIA-FLORALIS - THE ROLE OF GLUCOSINOLATE AND NONGLUCOSINOLATE COMPOUNDS

The role of leaf surface compounds influencing the oviposition of the turnip root By, Delia floralis, was investigated using bioassays and f ractionation of leaf surface extracts from four Brassica genotypes. Po lar leaf surface extracts contained between 65 and 175 nM/g leaf equiv alent of glucosinolates. However, following fractionation it Was found that nonglucosinolates were the major stimuli for D. floralis oviposi tion. Electrophysiological studies of leaf surface extracts and their fractions were performed by using D. radicum, the cabbage root fly, as an analytical tool. The most behaviorally active fractions contained stimulatory compound(s) that had an activity profile identical to that previously described for recently discovered nonglucosinolate compoun ds. The role of leaf surface chemicals in influencing antixenotic resi stance to D. floralis is discussed.