Journal
JOURNAL OF CHEMICAL ECOLOGY
Volume 36, Issue 3, Pages 277-285Publisher
SPRINGER
DOI: 10.1007/s10886-010-9758-6
Keywords
Barbarea vulgaris; Brassicaceae; Flea beetle; Phyllotreta nemorum; Chrysomelidae; Alticinae; Host plant resistance; Host shift; Deterrents; Triterpenoids; Saponins; Hederagenin cellobioside
Categories
Funding
- Danish Natural Science Research Council [21-02-0534]
- Danish Agency for Science, Technology and Innovation [274-06-0370]
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Three saponins and two sapogenins had differential effects on food consumption in five near-isogenic flea beetle lines, which differ in their ability to utilize a novel host plant, Barbarea vulgaris (Brassicaceae). The ability to live on this plant is controlled by major, dominant R-genes in the flea beetle, Phyllotreta nemorum (Coleoptera: Chrysomelidae: Alticinae). A susceptible genotype (rr) is unable to live on the plant, whereas resistant genotypes (RR and Rr) can utilize the novel host plant. Among compounds isolated from B. vulgaris, hederagenin cellobioside (hederagenin-3-O-(4-O-beta-D-glucopyranosyl)-beta-D-glucopyranoside) inhibited feeding, whereas the effect of oleanolic acid cellobioside was much weaker. The aglycones (sapogenins) were inactive. Although hederagenin cellobioside was active against all flea beetle lines, its effect on food consumption was much stronger on the susceptible genotype (rr) compared to the resistant genotype (Rr). Susceptible and resistant flea beetle genotypes were equally sensitive to a non-host saponin, alpha-hederin (hederagenin-3-O-(2-O-alpha-L-rhamnopyranosyl)-alpha-L-arabinopyranoside). These results suggest that R-alleles in flea beetles might be specific adaptations to defensive saponins in B. vulgaris. A possible mechanism of action of the R-alleles might be to encode for an enzyme (e.g. a glucosidase), which is able to cleave glycosidic bonds in hederagenin cellobioside, but not in alpha-hederin. The potential role of saponins as defensive compounds in B. vulgaris and as targets for counter-adaptations in flea beetles and other insects is discussed.
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