Behavioural and physiological responses of insects to climate change and consequences at the community level: the example of a host-parasitoid system in cereal fields Prof. Joan Van Baaren University of Rennes 1, UMR-CNRS 6553, ECOBIO, Rennes, France

Multiple responses to climate change are observed in animals, such as modifications of their morphology, physiology, behavioural strategies or phenology. Most of the responses involve phenotypic plasticity rather than genetic evolution. The responses at the individual level could impact the interactions within species (like competition) or between species at the trophic (prey-predators, host-parasitoid) and non trophic (interspecific competition) levels. In temperate areas, insects can escape the stressful winter conditions either by (1) migration, (2) diapause (i.e. arrest of development) or (3) remaining in activity by producing cryoprotectant molecules. Over the last 30 years, we observed a change in overwintering strategies of insects in cereal fields in western France, with fewer and fewer species entering diapause and changes in thermotolerance (physiology) and behaviours. This increase of winter activity at the individual level has cascading consequences on community structure and ecosystem functions. These consequences include an increasing competition between species, an increasing complexity of trophic web structures and modifications of the biocontrol ecosystem service. In agrosystems, the increase in non-crop plant diversity by habitat management in or around arable fields contributes to improve Conservation Biological Control. During winter, plants such as mustard are often used as monospecific ground cover and are expected to die before flowering as a result of recurrent frost events. Decreases in minimal temperature due to climate change offer new possibilities for plants used in such sown cover crops to mature and flower. Changes in plant phenology thus constitute an important environmental change with expected consequences for ecosystem functions such as biological control. Increasing floral diversity in sown cover crops could constitute a complementary method in management programs, by providing more alternative food resources, alternative hosts, and climatic refuge to enhance the Conservation Biological Control of parasitoid populations. .