Plants of the Salicacea genus have in common that they utilize phenolic glycosides, so called salicinoids, as protection against leaf chewing herbivores. The caterpillar Cerura vinula only feeds on poplar and willow trees that belong to the family of Salicacea. For this reason, Cerura vinula is viewed as a specialist herbivore that is adapted to the salicinoid defense. Taking advantage of chemical and biochemical techniques we want to trace the salicinoid metabolism pathway, the location of transformation and the involved enzymes. To gain insights into the salicinoid metabolism the caterpillars were put on a specially designed diet. It consisted either of one salicinoid in large excess or one 13C labelled compound, applied together with fresh poplar leaves. As a next step, we are going to identify the new compounds formed in the caterpillar by MS and NMR techniques. To determine the location and mechanism of the transformation we started with a dissection of the caterpillar and a check of the tissue pH value. Afterwards, we incubated the midgut, hindgut and salivary gland tissues with salicin as model substrate and analyzed the transformation products by LC-MS. The transformation products resulted from deglycosilation of the substrate and consecutive oxidation and conjugation of the aglycon. With the gained knowledge we then aimed to identify the enzymes, which are involved in the metabolism. We successfully proofed the existence of glucosidases in the midgut by isoelectric focusing and incubation of the gel with the model substrate 4-methylumbelliferyl β-D-glucopyranosid. Additionally, we performed RNA sequencing on the caterpillar tissue. The transcripts and enzymes involved in the salicinoid metabolism are currently analyzed. During our studies we could determine the mid gut as the place for the deglycosilaton, oxidation and conjugation of salicinoids. Further we identified a new for Cerura vinula undescribed metabolite and proofed the presence of β-glucosidases in the midgut.

In Europe, the cabbage stem flea beetle (Psylliodes chrysocephala) is a specialized insect feeding on Brassicaceae plants. The plants use the glucosinolate-myrosinase defense system, but P. chrysocephala can overcome this chemical defense by detoxification of the emerging ITCs by conjugation with glutathione (mercapturic acid pathway). In addition to known products of the mercapturic acid pathway, previously unreported metabolites were isolated, and their structures were elucidated by means of high resolution mass spectroscopy (HR-ESITOFMS) and nuclear magnetic resonance (NMR). The products found may represent general detoxification products of the mercapturic acid pathway.

Insect metabolism and the inter-species communication among insects are fascinating fields of science. The underlying chemical principles are difficult to elucidate since minute amounts of chemicals, often of unknown structures, are involved. The talk highlights recent examples of work where chemical analysis and biological research went hand in hand to unravel ecological mysteries. Focus will be on the use of modern and sensitivity improved nuclear magnetic resonance (NMR) spectroscopy serving as analytical key technology.