A Y-tube behavioral bioassay was developed to investigate attraction of the diamondback moth,Plutella xylostella(L.), to volatiles from host plants. During the scotophase, male and female moths were attracted to volatiles of homogenized leaves of Oriental mustard,Brassica juncea(L.) Cosson, plants at the flower bud stage, and to the odor of Oriental mustard seedlings. The response of both sexes increased with age from 1 to 7 d. Females were more strongly attracted when they were allowed prior access to both mates and plants, but the effect of these factors on males was ambiguous. Neither sex responded to volatiles during the latter half of the photophase. Females that responded to volatiles in a standard bioassay subsequently laid more eggs than did nonresponders and yet still contained similar numbers of mature eggs in their ovaries. This implies that egg load is related to responsiveness to plant volatiles. The patterns of response are interpreted in relation to reproduction in this species.