To ward off an attack by herbivorous insects, plants produce a variety of toxic or repulsive compounds. However, specialized insects have developed counter-strategies to deal with these defence compounds, which explains why many of these insects have become agricultural pests. It is becoming increasingly clear that these plant-insect interactions can only be understood by investigating the function of plant toxins from the perspective of the plant and the insect simultaneously. In a preliminary study carried out in the FARCE laboratory at the University of Neuchâtel, we have demonstrated that benzoxazinoids (BXDs), a specific class of nitrogen-containing secondary metabolites produced by grasses, strongly affect the metabolism, the behaviour and the fitness of an important, highly specialized pest of maize: caterpillars of the moth Spodoptera frugiperda. We have found that maize changes its BXD production after detecting caterpillar feeding, and that Spodoptera frugiperda has evolved mechanisms to circumvent their negative effects. The BXD-mediated interaction between maize and Spodoptera caterpillars complex an ideal model to study the role of plant secondary metabolites at the interface between plants and insects. The current project brings together knowledge from molecular biology, plant and insect biochemistry, phytochemistry, ecology and behaviour, as well as agricultural sciences to track the fate of BXDs from their production in the plant to their conversion inside the target insect. By using such a highly interdisciplinary, cross-species approach we will be able to elucidate the precise role of BXDs in plant-insect interactions. As BXDs consume a significant fraction of the nitrogen available to a plant, but at the same time serve as a potentially important barrier against pests, our study goes beyond purely fundamental research and opens up interesting possibilities for application in agriculture. The project is headed by UniNE, represented by the FARCE laboratory and the Analytical Chemistry Service of the Swiss Plant Science Web, and involves partners from the Federal Research Station Agroscope Changins-Wädenswil, the University of Geneva and the Max Planck Institute for Chemical Ecology in Jena (Germany).