Physical and chemical factors influencing landing and oviposition by the cabbage root fly on host‐plant models

Various plant models were used in both choice and no‐choice tests in the laboratory to assess landing and oviposition preferences of the cabbage root fly, Delia radicum (L.). The main factor governing the site most suitable for landing was the conspicuousness of the object and not its shape. Oviposition was influenced considerably by the pre‐conditioning of the females. Deprived females laid eggs even when denied access to both host plant chemicals and host‐plant models. The dominant role of contact chemical stimuli in host acceptance was reconfirmed, but only a combination of physical and chemical stimuli appeared capable of eliciting normal oviposition. The combination of contact chemical stimuli and the presence of a stem on the test model had a synergistic effect on the numbers of eggs laid in both choice and no‐choice situations. In choice bioassays, female cabbage root flies distinguished between models of different shapes, heights and sizes. The size and shape of the models appeared to be perceived in part after the flies had landed.