HOST-FINDING AND UPWIND ANEMOTAXIS BY DELIA-ANTIQUA (DIPTERA, ANTHOMYIIDAE) IN RELATION TO AGE, OVARIAN DEVELOPMENT, AND MATING STATUS

A dual-port wind tunnel was used to test hypotheses that odor-mediated anemotaxis in the onion maggot, Delia antiqua (Meigen), to volatiles of onion, Allium cepa L., is affected by differences in age, sex, mate d status, and ovarian development. In the absence of odor and air move ment, adults of both sexes dispersed randomly in the wind tunnel. They displayed significant, albeit weak (approximate to 15%), anemotactic (upwind) response to air movement at 8.0 cm/s. In 12 h comparisons of virgin females tested at 2, 4, 6, 8, and 10 d of age with gravid, mate d females (10-12 d), anemotactic and discriminatory responses to onion odor of females aged 4-10 d were comparable (approximate to 30%), but were consistently lower than the responses of gravid, mated females ( approximate to 45%), Male upwind response to host odor increased linea rly with age over 10 d. When 10-d-old males were tested together with females in the wind tunnel, however, significantly fewer males were at tracted to onion than when females were absent. Ten-day-old protein-de prived virgin and mated females (both previtellogenic) responded to on ion odor in a similar manner as did gravid, mated females. The respons e of mated, 10-d-old previtellogenic females was lower than that of gr avid, mated females. We conclude that upwind response by D. antiqua to host odor is independent of female ovarian development or mated statu s. Such a response would serve to draw females to their oviposition si tes and may assist males in locating sites where females are likely to arrive.