COMPARATIVE-ANALYSIS OF HEADSPACE VOLATILES FROM DIFFERENT CATERPILLAR-INFESTED OR UNINFESTED FOOD PLANTS OF PIERIS SPECIES

Plants that are infested by herbivores emit volatile cues that can be used by the natural enemies of the herbivores in their search for host s. Based on results from behavioral studies, we investigated to what e xtent intact and herbivore-infested plant species and varieties from t he food plant range of Pieris herbivore species differ in the composit ion of the volatile blends. Parasitoids of Pieris species, Cotesia glo merata and C. rubecula, show differential responses towards various he rbivore-infested food plants, whereas differences in responses to plan ts infested by other herbivore species were less clear. Chemical analy sis of the headspace samples of red cabbage, white cabbage, and nastur tium plants that were infested by P. brassicae or P. rapae larvae, or that were intact, yielded 88 compounds including alcohols, ketones, al dehydes, esters, nitriles, terpenoids, sulfides, (iso)thiocyanates, ca rboxylic acids, and others. The analysis revealed that herbivore-infes ted plants emit the largest number of compounds in the highest amounts . The plant species affected the volatile blend more than did the herb ivore species, and differences between plant varieties were less prono unced than differences between plant species. Differences in headspace composition between plants infested by P. brassicae or P. rapae were mainly of a quantitative nature. Herbivore-infested nasturtium differe d considerably from the cabbage varieties in a qualitative way. Headsp ace compositions of red and white cabbage varieties were comparable to that of the food plant Brussels sprouts (Brassica oleracea gemmifera cv. Titurel) as determined in earlier studies in our laboratory. With respect to plant response to herbivory, nasturtium differed considerab ly from the cabbage varieties analyzed so far and shows resemblance wi th Lima bean, cucumber, and corn. These plant species produce a greate r quantity and variety of volatiles under herbivore attack than intact plants. The results of this study are discussed in relation to behavi oral observations on C. glomerata and C. rubecula.