rapid northward shift of the range margin of a Mediterranean parasitoid insect (Hymenoptera) associated with regional climate warming

AIM: Many species are undergoing range shifts to higher latitudes in response to global warming. Whereas several studies of insects have examined causes of variability in the rate of range expansions, few studies have investigated species occupying higher trophic levels, where the effects of climate change are predicted to be particularly strong. Here, we analyse changes in the geographical range of Leptopilina boulardi, a small parasitoid of Drosophila larvae, in relation to temperature changes in the study area. LOCATION: The Rhône–Saône Valley in south‐eastern France. METHODS: A survey of L. boulardi and its two Drosophila host species was conducted in 16 localities at the northern margin of the L. boulardi range over a period of 9 years. A generalized linear mixed model was used to explain the occurrence of the parasitoid in the study area and its northward progression. We also developed linear mixed‐effects models to determine the temperature changes in the studied area. RESULTS: Leptopilina boulardi was found to be moving very rapidly northwards, with an average rate of range expansion of 90 km decade⁻¹, exceeding previously observed rates for small insects. We recorded significant warming (+1.57 °C, on average from 1979 to 2011), with a considerable temperature increase of 4 °C in the spring. Leptopilina boulardi range expansion is not limited by host availability, and we suggest that this northward range expansion is primarily a direct response to climate warming. MAIN CONCLUSIONS: In south‐eastern France, a very rapid progression northwards, which coincides with a marked increase in temperature, was observed for a higher‐trophic‐level insect.