Extracting oviposition stimulants for carrot fly from host-plant leaves

Extracts of carrot foliage obtained with various extraction methods were compared for effectiveness in stimulating oviposition in the carrot fly. In choice assays, surrogate leaves treated with a hexane surface extract produced with a new microwave-assisted procedure were almost as acceptable as real host leaves. The high stimulatory activity of this extract was attributable to the raised solvent temperature, since cold hexane extracts were much less stimulatory. The microwave extract elicited about twice as much oviposition as the previously used dichloromethane surface extracts and the diethyl ether fraction of an extract that was obtained by brief immersion of leaves into water near its boiling point. The ovipositional responses to crude methanol and hot water extracts were weak because of the presence of yet unidentified polar deterrent compounds. Total extracts of ground foliage (vacuum distillation and extraction with liquid carbon dioxide) had no net stimulatory effect on oviposition.