Extracting oviposition stimulants for carrot fly from host-plant leaves

Extracts of carrot foliage obtained with various extraction methods were co mpared for effectiveness in stimulating oviposition in the carrot fly. In c hoice assays, surrogate leaves treated with a hexane surface extract produc ed with a new microwave-assisted procedure were almost as acceptable as rea l host leaves. The high stimulatory activity of this extract was attributab le to the raised solvent temperature, since cold hexane extracts were much less stimulatory. The microwave extract elicited about twice as much ovipos ition as the previously used dichloromethane surface extracts and the dieth yl ether fraction of an extract that was obtained by brief immersion of lea ves into water near its boiling point. The ovipositional responses to crude methanol and hot water extracts were weak because of the presence of yet u nidentified polar deterrent compounds. Total extracts of ground foliage (va cuum distillation and extraction with liquid carbon dioxide) had no net sti mulatory effect on oviposition.