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Foliage of twelve host and two non-host species and surrogate leaves treated with the respective leaf extracts were presented to laboratory populations of the carrot fly (Psila rosae) in oviposition choice assays. The stimulatory activity of dichloromethane surface extracts and the diethyl ether fraction of hot water extracts did not reflect accurately the differences in acceptability observed among intact leaves. A better correlation was found using hexane extracts prepared in a microwave oven. Two out of five fractions of this crude hexane extract obtained by silica gel column chromatography stimulated oviposition. The diethyl ether fraction, which contained the previously identified oviposition stimulants (propenylbenzenes, furanocoumarins, polyacetylenes), could account for only a minor part of the variation in the acceptability of host leaves. The preference hierarchy for intact leaves corresponded better to the ranking of species according to activity of the methanolic fraction, which apparently contains unknown stimulatory compounds.¶ The water fractions of the hot water extracts were shown to reduce egg-laying underneath surrogate leaves treated with a stimulatory extract. This oviposition-deterring effect was particularly strong with the non-preferred species Pimpinella major, which is also highly resistant in the field. Hence, unidentified inhibitory compounds may also contribute to differential accept ability of host plants. It is concluded that antixenotic (non-preference) resistance of host plants to carrot fly attack depends on complex mixtures of semiochemicals.

A leaf-differentiating tissue culture which produced substantial amounts of pseudoisoeugenol- (2-methylbutyrate) has been used to examine the origin of the pseudoisoeugenol skeleton. 14Cand 13C-labelling revealed ʟ-phenylalanine, trans-cinnamic acid and p-coumaric acid as precursors. 13C-labelled precursors proved to be especially useful.

The roots of Pimpinella major Huds., P. saxifraga L. and P. peregrina L. do not contain any of the furocoumarins, indicated in previous literature. The main components of roots and fruits of P. major and P. saxifraga are isoeugenol epoxy tiglic ester, isoeugenol epoxy-2-methyl butanoic ester and 4-(1′,2′-epoxypropyl)-phenyl tiglic ester. The fruit and roots of P. peregrina do not contain these components. Only the fruit of P. major contains β-bisabolene and larger amounts of bisabolangelone.