Ph.D. research

Ph. D. project: Diapause variability in aphid parasitoids in a climate-change context; implications for biological pest control.

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Climate change effects are more and more dramatic on organisms. They affect their geographic range, abundance and ecology. In particular, climate warming leads to warmer, shorter and later winters which disrupt organisms' phenology. As ectothermic animals, insects are a particularly sensitive group to any change of the thermal environment and in particular any change in seasonal temperature variations. Indeed, insects usually overwinter as diapausing individuals. Yet, an increasing number of studies suggest that overwintering strategies, such as diapause, are highly influenced by current climate-changes. In numerous insect species, a "loss of diapause" strategy seems to spread out. 

Since 2010 in Western France, a major change in aphid parasitoids relative abundances has been detected in cereal crops during winter. Some parasitoid species that were never observed before during winter (suggesting that they were in diapause) are now active during this season and exploit anholocyclic aphids as hosts. These modifications in insect communities seem to be linked to a softening of winter temperature and suggest that the diapause strategy has been abandoned in these parasitoids populations experiencing mild winters. A shift in overwintering strategy can have unpredictable consequences on parasitoids community and food-web functioning and may impair natural biological control of aphid pests. In colder areas such as Canada, the loss of diapause is currently not possible, which allows us to compare different populations adapted to either mild or harsh winter climates.

The general objective of this PhD project is to understand the physiological and evolutionary mechanisms linked to the loss of phenotypic expression of diapause in parasitoids, and to evaluate the potential consequences on aphid populations and food-web functioning. To do so, I used both field, laboratory and modeling approaches. My results can translate to other insects in which similar responses to climate change are expected. This study focuses on cereal aphid parasitoids of the genus Aphidius that are present in both Québec and France.

Experimental and methodological approaches include; (i) field sampling and insects monitoring in Britanny (species relative abundances, diapause levels in winter depending on meteorological conditions) and aphid-parasitoids food-web characterization across the years; (ii) analyze of the diapause-inducing stimuli in aphid parasitoids and identification of the main mechanisms through which climate-change can act on diapause expression (temperature, maternal effects, hosts); (iii) analyze of evolutionary mechanisms (phenotypic plasticity, genetic adaptation) involved in changes of phenotypic expression of the diapause strategy.

Results from these three major research axes will highlight if changes in parasitoid community composition are actually linked to climate-changes and to better understand the ecological and evolutionary mechanisms involved in the current change in diapause expression. This work will forward help evaluate and predict the impact of current and future climate-change on insects seasonal ecology. Our results will eventually lead to the estimation of consequences of such changes on natural biological control of crop pests and highlight economic and societal implications in both France and Canada.