The decision to reject an oviposition site: sequential analysis of the post-alighting behaviour of Delia floralis

The post-alighting behaviour of gravid female turnip root fly Delia florali s (Fallen) (Diptera: Anthomyiidae), was observed in the laboratory, using f our plant genotypes differing in antixenotic resistance, to stimulate a ran ge of oviposition-related behavioural events. Analysis of the behavioural s equences of individual female flies suggested that during the post-alightin g behaviour of D. floralis, the decision to reject a highly resistant plant was predominantly based on plant cues received during a stationary period immediately after landing on the leaf (the leaf contact phase). Female flie s that rejected a plant immediately after the leaf contact phase did so aft er spending approximately twice as long in the leaf contact phase as those flies that continued to explore the plant. On a plant genotype of intermedi ate susceptibility, D. floralis females on the stem of the plants increased proboscis extension. The mechanisms involved in early host plant rejection decisions and the possible ecological advantages of such behaviour pattern s to female flies seeking suitable oviposition sites are explored. The pote ntial advantages of using detailed studies of individual behaviour sequence s to focus studies seeking to elucidate chemical oviposition stimuli on the plant's surface are also discussed.