The terrestrial vegetation releases a large variety of volatile organic compounds that constitute complex olfactory environments (odorscapes). These volatile plant compounds (VPC) play major roles as infochemicals mediating the interactions between organisms. Insects for instance extract from their odorscapes cues essential for their reproduction. Mate or host-plant finding behaviors are largely based on the perception of specific odor signals by their sensory system. There is conclusive evidence that the specialized receptors that detect the behavior-relevant odorants are sensitive to odor background. With the growing likelihood of a rapidly changing environment due to the anthropogenic emissions of greenhouse gases, the composition of future odorscapes in agro-ecosystems will largely depend on the sensitivity of VPC production to single or combined component(s) of global climatic change. Yet, the impacts of such predicable profound changes in odorscapes on insect olfaction have not been properly evaluated. Our project aims at:

1) evaluating qualitatively and quantitatively the effects of major environmental change components on metabolic pathways and emission of VPCs by crop and companion plants in two ecosystems representative of dry and humid temperate agro-ecosystems;

2) analyzing the effects of the altered odorscapes on olfaction of herbivorous insects at gene, neural coding and behavior levels.

We will analyze the volatile emissions from plants associated in mini ecosystems typical for two different climatic conditions present in France: a dry temperate climate (DT) and a humid temperate climate (HT). Each mini ecosystem will consist of a cultivated plant (corn), a tree (poplar for HT or oak for DT) and a weed which will be grown in controlled conditions under CO₂, O₃, drought and temperature levels representative of global change. The effects of growing conditions on the main metabolic pathways involved in the production of VPCs will be analyzed. We expect that the volatile emissions from DT and HT under elevated global change factors will affect female choices for oviposition sites and male responses to sex pheromone. Thus, we will identify the natural emissions in two growing conditions, measure the response of insects and reconstitute behaviorally effective modified odorscapes HTO and DTO. The effects of HTO and DTO and their major components on olfactory coding within the antennae and the primary olfactory centres, the antennal lobes, will be investigated. The ability of insects to adapt their behavior to changes in their sensory environment will be evaluated by investigating behavioral plasticity. The effects of long-term exposure to reconstituted odorscapes on the expression of olfactory genes within the antennae will then be tested.

Our project will lead to a deeper understanding of the vulnerability to environmental changes of information exchanges inside agro-ecosystems, of the adaptive capacities of plants and insects to global changes and of their potential consequences for the functioning of agro-ecosystems. The expected results will contribute to a better predictability of the evolution of agro-ecosystems under anthropogenic influence and will also have an impact on applied aspects, taking into account that pheromones and plant odorants are used as alternative control measures for insecticides.