Carrot fly cultivar preferences: some influencing factors

Abstract. 1. Factors affecting cultivar preferences by the carrot fly Psila rosae F. were examined in choice tests using foliage from carrot lines representing extremes of resistance and susceptibility to attack.
2. Flies were offered a choice to oviposit on foliage, artificial substrates impregnated with leaf surface extracts or enclosed in vapours of different cultivars to establish the importance of contact and olfactory stimuli. Susceptible cv. Danvers Half Long 126 foliage was preferred over that of resistant cvs. Clause's Sytan Original and Tip-Top. But, whereas the Sytan leaf surface extract was as effective as that of Danvers, the surface extract of Tip-Top was very much inferior as an oviposition stimulant. By contrast, Sytan and Tip-Top foliar vapours were both more attractive to the fly than that from Danvers.
3. Headspace vapours over Sytan foliage evoked significantly higher electroantennogram responses than those from Danvers.
4. Cold-trapped foliar volatiles of Sytan and Danvers were analysed by gas chromatography linked with antennographic detection. Foliage of Sytan released, among other chemo-stimulants, higher levels of host plant attractants, i.e. green leaf aldehydes and the phenylpropanoids, trans-asarone and trans-methylisoeugenol.
5. These findings indicate that olfactory and contact chemostimuli may be involved in preferences shown by the carrot fly for carrot cultivars, but these factors alone do not fully account for the preferences observed.