IDENTIFICATION OF OLFACTORY CUES USED IN HOST-PLANT FINDING BY DIAMONDBACK MOTH, PLUTELLA-XYLOSTELLA (LEPIDOPTERA, PLUTELLIDAE)

Olfactory attraction of female diamondback moths (Plutella xylostella) to odors of intact and homogenized host plants, as well as individual compounds characteristic of host plants, were investigated by behavio ral and electrophysiological methods. Moths were attracted to odors of Brassica juncea and B. napus seedlings in a Y-tube bioassay. Solvent fractions of homogenized B. juncea leaves were attractive to moths whe ther or not isothiocyanates (IC) were present. Moths were attracted in Y-tube bioassays and to field traps baited with individual ICs. Volat iles from B. juncea and B. napus elicited an electroantennogram (EAG) response and were attractive in the Y-tube bioassay. Allyl IC was show n to be the attractive component in homogenized plant volatiles but wa s found to be virtually absent from intact plant volatiles. Gas chroma tographic fractionation of intact plant volatiles revealed a terpene-c ontaining fraction to be most attractive to the moths. We were unable to isolate individual attractive compounds from this fraction. Our res ults suggest that certain elements of this fraction, possibly in combi nation, are important olfactory cues for host-plant finding by the dia mondback moth with mustard oils playing an important and possibly syne rgistic role, particularly when plants are damaged.