Oviposition behavior of the cabbage root fly,Delia radicum (L.), influenced by host plant extracts

An ethanolic extract of cabbage leaves (Brassica oleraceavar. capitata,Golden Acre)and derived fractions were tested on natural and surrogate leaves in order to study the oviposition behavior of the cabbage root fly Delia radicum(Diptera: Anthomyiidae). On surrogate plastic leaves coated with a thin layer of paraffin wax and treated with 0.1 gram leaf equivalent (gle) of an ethanolic raw cabbage extract, the females displayed the same sequence of behavioral patterns as on a natural host plant. The quantified oviposition behavior correlated well with the actual number of eggs laid. The extract-treated surrogate leaves received at least as many eggs as natural leaves with a similar surface area. Previous exposure to surrogate or natural leaves seemed not to induce a specific preference. The three fractions (hexane, butanol, and water) of the raw extract stimulated the oviposition behavior. This was taken as evidence for the presence of a multicomponent mixture or a chemical pattern in the cabbage leaves stimulating oviposition. At the tested concentration each fraction alone could stimulate in some individuals the complete behavior. No effect of volatile components of the raw extract could be detected. This is thought to be due to the extraction procedure, which limits the production of attractive, volatile compounds, such as isothiocyanates.