Vol.:(0123456789) 1 3 Arthropod-Plant Interactions https://doi.org/10.1007/s11829-018-9633-x ORIGINAL PAPER Diferent herbivore responses to two co-occurring chemotypes of the wild crucifer Barbarea vulgaris Stina Christensen 1  · Swantje Enge 1,3  · Karen Rysbjerg Jensen 1  · Caroline Müller 2  · Lars Pødenphant Kiær 1  · Niels Agerbirk 1  · Christine Heimes 1  · Thure P. Hauser 1 Received: 2 February 2018 / Accepted: 23 August 2018 © Springer Nature B.V. 2018 Abstract According to coevolution theory, plant chemical defences are continually evolving in response to selection by herbivores. Unique to the Brassicales, a few species in the Barbarea genus produce triterpenoid saponins that are highly deterrent to some specialist insect herbivores. One species, B. vulgaris, has diverged into two chemotypes, the G- and P-type, of which the P-type seems to have lost the saponin-based insect resistance by producing diferent saponin structures; it also produces diferent glucosinolates and other potential defence traits. Here, we examined the preference and performance of a larger set of specialist and generalist herbivores on the two plant types, including three generalist mollusc (Arion vulgaris, Deroceras sp., Cepaea sp.) as well as three specialist (Phaedon cochleariae, Athalia rosae, Pieris napi oleraceae) and two generalist (Mamestra brassicae, Myzus persicae) insect herbivores. Five out of six herbivore species preferred leaves of the P-type for feeding, and most of them also survived and/or grew better on the P-type, or preferred it for oviposition. In contrast, larvae of M. brassicae showed no preference and performed equally well on the two plant types; the leaf beetle P. cochleariae preferred the G-type for oviposition, which was, however, not refecting larval performance. Overall, the defences of the P-type against herbivores seem not to be as efective as those of the G-type, which is surprising given its large geographi- cal distribution, overlapping with that of the G-type in Scandinavia and Finland. This suggests that additional ecological interactions determine the success of the two chemotypes. Keywords Feeding preference · Oviposition preference · Defence compounds · Glucosinolates · Saponins Introduction According to coevolution theory, the immense diversity of specialised metabolites in plants mainly evolved to reduce or avoid damage from herbivores and pathogens. Many of these metabolites afect a limited array of potential antago- nist species, as some antagonists have subsequently evolved resistance to these, and other antagonists probably never were afected. Thus, for a given chemical defence at a given time and place, we should expect to see a range of efects on potential antagonists of various kinds and phyla. The large and economically important Brassicales order is generally characterised by its chemical content of glu- cosinolates, which afect a diverse range of herbivores and pathogens. Around 142 diferent chemical structures have so far been documented, and new structures are still being dis- covered (Agerbirk and Olsen 2012; Olsen et al. 2016). Many plant antagonists have, however, evolved resistance towards glucosinolates in general, allowing them to specialise on Handling Editor: Miriama Malcicka. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11829-018-9633-x) contains supplementary material, which is available to authorized users. * Thure P. Hauser tpha@plen.ku.dk 1 Copenhagen Plant Science Centre, Department of Plant and Environmental Sciences, University of Copenhagen, Frederiksberg, Denmark 2 Department of Chemical Ecology, Bielefeld University, Bielefeld, Germany 3 Institute for Chemistry and Biology of the Marine Environment, Carl-von-Ossietzky University Oldenburg, Oldenburg, Germany