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 behavioral 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 whether or not isothiocyanates (IC) were present. Moths were attracted in Y-tube bioassays and to field traps baited with individual ICs. Volatiles from B. juncea and B. napus elicited an electroantennogram (EAG) response and were attractive in the Y-tube bioassay. Allyl IC was shown to be the attractive component in homogenized plant volatiles but was found to be virtually absent from intact plant volatiles. Gas chromatographic fractionation of intact plant volatiles revealed a terpene-containing fraction to be most attractive to the moths. We were unable to isolate individual attractive compounds from this fraction. Our results suggest that certain elements of this fraction, possibly in combination, are important olfactory cues for host-plant finding by the diamondback moth with mustard oils playing an important and possibly synergistic role, particularly when plants are damaged.