Long-range host-finding behaviour of the onion fly Delia antiqua (Diptera: Anthomyiidae): ecological and physiological constraints.
The long-range, host-finding behaviour of Delia antiqua was investigated in 16 mark-release-recapture experiments in Canada using onion-reared flies from a facultatively diapausing, laboratory colony. In general, adults dispersed uniformly in fallow, bare soil and grass fields devoid of host-plant stimuli. The rate and direction of dispersal were unaffected by the sex, age or mating status of flies and independent of the prevailing wind directions. In fields permeated with dipropyldisulfide (DPDS), a volatile from host Allium spp., virgin flies dispersed randomly until they reached reproductive maturity (about 4 and 7 days old for males and females, respectively) after which they exhibited directional movement and positive anemotaxis. Dispersal by mated, gravid females in habitats containing a uniform, high concentration of DPDS was slow and non-directional in comparison with virgin, gravid females. Non-host, grass vegetation markedly reduced mated female recapture on DPDS-baited traps. Patterns of mated female recapture suggested that they did not use odour-mediated, positive anemotaxis to locate sources of DPDS in vegetated habitats permeated with DPDS although positive anemotaxis was detectable in bare-soil fields containting DPDS. It is suggested that long-range orientation by D. antiqua towards host-plants, at the habitat and patch levels of foraging, involves positive anemotaxis in response to host-plant-produced alkyl disulphides.