Beata Szafranek

Leaf surface compounds of the potato (Solanum tuberosum) and their influence on Colorado potato beetle (Leptinotarsa decemlineata) feeding

Summary.The sampling behavior of the Colorado potato beetle Leptinotarsa decemlineata Say (CPB) involves examination of the surface of potato leaves. It has been suggested that leaf surface compounds (volatiles and cuticular waxes) may be involved in host-plant recognition, acceptance or discrimination. Here we report on the effect of leaf surface extracts of six Polish commercial potato varieties on CPB feeding. We tested the influence of potato leaf surface extracts on CPB adult and larval feeding, then separated the extracts with HPLC, and finally tested the effect of the HPLC-separated fractions on CPB feeding. The bioassays were performed using potato leaf discs deprived of their original surface compounds. Applied to test discs at concentrations ten times higher than natural (10 leaf area equivalent), the extracts deterred CPB adults and larvae from feeding. HPLC-separated fractions composed of alkanes, sesquiterpene hydrocarbons, wax esters, benzoic acid esters, fatty acid methyl, ethyl, isopropyl and phenylethyl esters, aldehydes, ketones, methyl ketones, fatty acids, primary alcohols, β-amyrin and sterols did not affect adult CPB feeding. Similarly, alkanes, sesquiterpene hydrocarbons, wax esters, methyl ketones, sesquiterpene alcohols and secondary alcohols had no effect on larval CPB feeding. The sterol fraction (cholesterol, β-sitosterol and stigmasterol) acted as a phagostimulant to CPB larvae. We isolated a fraction demonstrating a phagodeterrent effect on CPB adults and larvae. The qualitative composition of the deterrent fraction was quite similar in all potato extracts, but there were quantitative differences between the varieties. Much further work is needed to identify the compounds that can produce the deterrent effect.

The sesquiterpene composition of leaf cuticular neutral lipids of ten Polish varieties of Solanum tuberosum

The sesquiterpene composition of leaf cuticular neutral lipids of potato (Solanum tuberosum) varieties was investigated by GC, GC-MS and HPLC. The distribution of sesquiterpenes varied between varieties with the major components being beta-caryophyllene, trans-beta-farnesene, germacrene D, beta-sesquiphellandrene and germacrene D-4-ol. cis-beta-Farnesene and bicyclogermacrene were identified in potato for the first time. The amount of sesquiterpenes was 10-60% of the cuticular neutral lipids depending on variety. The sesquiterpenes and alkanes were the major groups of components in the waxes investigated.

Gas Chromatographic Analysis of Plant and Insect Surface Compounds: Cuticular Waxes and Terpenoids

The surfaces of all higher plants are covered by a layer of cuticular waxes. These are composed mainly of long-chain aliphatic components but also of cyclic compounds. The primary role of the waxes is to prevent uncontrolled water loss. The chemical composition of plant cuticular waxes can affect the resistance of plants to herbivores and herbivore behaviour. Cuticular waxes and their separate components enhance or deter insect oviposition, movement or feeding.