Host-plant susceptibility to the carrot fly, Psila rosae. 1. Acceptability of various host species to ovipositing females

A preference hierarchy of the oligophagous carrot fly for 30 umbelliferous host-plant species or varieties and six non-hosts was assessed. Foliage of the test plants was presented to a laboratory population of the fly in oviposition choice experiments together with leaves of a standard plant, the susceptible carrot cultivar “Danvers”. Only two species (Anthriscus cerefolium, Carum carvi) were more acceptable than the standard plant, while about half the species received significantly fewer eggs. Some umbellifers (Anethum graveolens, Pimpinella major) had a low acceptability similar to that of non-hosts (non-umbelliferous plants). The results obtained with dual and multiple choice assays were in agreement. A multiple choice assay with potted plants yielded a similar ranking of the species as assays using detached leaves, indicating that foliage is representative for whole plants. Variability in the exploratory runs performed by the females on the leaves prior to egg-laying is described and quantified for hosts and non-hosts. Differences in post-alighting pre-ovipositional behaviour of the female flies on the leaves accounted for a major part of the variation recorded in egg-laying.