COMPARATIVE HEADSPACE ANALYSIS OF CABBAGE PLANTS DAMAGED BY 2 SPECIESOF PIERIS CATERPILLARS - CONSEQUENCES FOR IN-FLIGHT HOST LOCATION BY COTESIA PARASITOIDS

Headspace composition, collected from intact cabbage plants and cabbag e plants infested with either Pieris brassicae L. or P. rapae L. (Lepi doptera: Pieridae) first instar larvae, was determined by GC-MS. Twent y-one volatiles were identified in the headspace of intact plants. Twe nty-two volatiles were identified in the headspace of plants infested by P. brassicae larvae, 2 of which, Z-3-hexenyl butyrate and Z-3-hexen yl isovalerate, were not detected in the headspace of either intact or P. rapae damaged plants. In the headspace of the latter, 21 compounds were identified, all of which were also produced by intact plants. No significant quantitative differences were found between headspace com position of the plants damaged by one or the other caterpillar species . Major differences between intact and caterpillar-damaged plants in c ontribution to the headspace profile were revealed for hexyl acetate, Z-3-hexenyl acetate, myrcene, sabinene and 1,8-cineole. The larval end oparasitoid Cotesia glomerata L. was attracted by the volatiles emanat ing from B. oleracea damaged by brassicae first instar larvae. C. rube cula L., a specialized larval endoparasitoids of P. rapae, was attract ed by the volatiles released from the B. oleracea -P. rapae plant-host complex. This shows that cabbage plants kept under the conditions of headspace collection produce attractive volatiles for both parasitoids .