Biologie des organismes et des populations appliquée à la Protection des plantes

Agricultural landscapes are characterised by several spatial units fairly stable through time. A Cereal crop is one of them. Food is concentrated within it but available few months only. Species exploiting such ephemeral habitats exhibit adaptations. For example, they regularly emigrate and colonise new habitats.

Aphids are good colonizers as they produce winged individuals and multiply rapidly by parthenogenetic reproduction.

I have studied population functioning in agricultural landscape of the aphid Sitobion aveane, an important pest on cereal in Europe.

I have followed, during spring and summer, both colonization and establishment of populations on wheat and studied whether natural enemies mediates these processes under laboratory conditions.

I have showed that wheat continuously receive migrants that didn’t succeed in establishing large colonies until wheat have reached a given developmental stage. There were two genetic pools of aphids on grasses. I also founded that natural enemy, here parasitoids, influenced the colonization process through the demography and life history traits of the colonizers. They also shape the spatial distribution of individuals.

The genetic structure may reflect different strategies used by aphids to exploit ephemeral habitats. One of them consist in migrating between crops all over the year, the other one consist in making several migration between crops in spring and uncultivated habitats in winter. This can isolate populations during the occasional sexual events in fall and winter if individuals can’t freely switch between both strategies. Such a metapopulation functioning can cause spatial variation in natural selection and gene flow across a farming landscape and shape local coevolutionary dynamics between host plant, pest and their natural enemies. This could maintain a high level of phenotypic and genotypic diversity on crops.