Patterns of oviposition stimulants for carrot fly in leaves of various host plants

Undamaged leaves of 12 host-plant species differing widely in acceptability to ovipositing carrot flies were extracted with a microwave-assisted metho d with hexane as solvent. The highly stimulatory diethyl ether fraction obt ained by separation on a silica gel column was semiquantitatively analyzed by CC-MS for previously identified oviposition stimulants of the carrot fly (phenylpropenes, fluranocoumarins, polyacetylenes). Various plant species exhibited widely differing profiles of these compounds. In choice assays, m oderate numbers of eggs were deposited underneath surrogate leaves sprayed with fractions that contained high amounts of just one type of compound and low amounts of the other two types. Only fractions with medium to high lev els of at least two compound classes elicited strong ovipositional response s (e.g., phenylpropenes and polyacetylenes in Daucus carota, furanocoumarin s and polyacetylenes in Heracleum sphondylium and Conium maculatum). None o f the examined plants contained high quantities of all three compound class es. The contents of the stimulants seemed to account in a synergistic manne r for the variation in activity of the diethyl ether fraction. However, the y could not explain adequately the observed preference hierarchy of the car rot fly for the host-plant species.