Host Rejection of the White Mustard (Sinapis alba) by a Major Oilseed Rape Pest Is Driven by the Avoidance of...

A key postulate in chemical ecology is that specialist herbivore insects have evolved abilities to tolerate chemical defenses specific to their host plants. Nevertheless, past studies have shown that this assumption does not always hold true. Identifying the compounds responsible for this occasional paradigm shift is essential for improving our understanding of plant-insect interactions, and for the development of new control strategies against specialized insect pests. In this study, we examined the relationship between the chemistry of Sinapis alba L. (Brassicales: Brassicaceae) and adult feeding in Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae), i.e., a Brassicaceae specialist and major oilseed rape pest. A variation in the ability of different S. alba cultivars to resist feeding by this insect pest was exploited to identify deterrent compounds. A comparative bioassay-guided fractionation approach led to the hypothesis that sinalbin, a glucosinolate specific to S. alba and few other brassicaceous species, might deter feeding of P. chrysocephala adults. Pure sinalbin was tested at various concentrations, confirming its deterrent effect at a concentration naturally found in leaves of two-week-old plants, i.e., 15 nmol.mg^- 1 FW. Such results provide new insights into host selection mechanisms of Brassicaceae specialists, i.e., that avoidance of intact glucosinolates may also contribute to preference. From an applied perspective, the identification of sinalbin as a biomarker of resistance in S. alba has the potential to guide future efforts into the development of new management strategies for oilseed rape pests such as P. chrysocephala.