Expansion of geographic range in the pine processionary moth caused by increased winter temperatures

Global warming is predicted to cause distributional changes in organisms whose geographic ranges are, at least in part, controlled by temperature. We report a recent latitudinal and altitudinal expansion of the pine processionary moth, Thaumetopoea pityocampa, whose larvae build silk nests and feed on pine foliage in the winter. In north-central France (Paris Basin), its range boundary has shifted by 87 km northwards between (1972 andto 2004); in northern Italy (Venosta/VinschgauAlps), the an altitudinal shift of corresponds to 110-230 m upwards occurred between( 1975 to and 2004), depending on the slope aspect. By experimentally linking winter temperature, feeding activity, and survival of T. pityocampa larvae, wWe attribute the expansions to increased winter survival due to the effects of the a warming trend in over the past three decades, by experimentally linking winter temperature, feeding activity and survival of T. pityocampa larvae. In the laboratory, we determined the minimum nest and night air temperatures required for larval feeding, and developed a simple mechanistic model based on these temperature thresholds. We tested the model in a translocation experiment that employed natural temperature gradients as spatial analogues for global warming. In all transects, we transferred colonies of T. pityocampa larvae to sites within zones of historical distribution, recent distribution, and outside the present range (northern- or uppermost). We monitored air and nest temperature, incoming solar radiation (insolation), and larval phenologyphenology, feeding activity, and survival. Early-season temperature effects on phenology were evident, with delayed development of colonies in the more extreme (colder) sites showing ed development. In the coldest months, our predictive model was consistent with the observed patterns of feeding activity: feeding was progressively reduced with increasing latitude or elevation, as predicted by the lower number of hours when the feeding threshold was reached, and negatively affected final survival. Insolation raised nest temperature and increased feeding activity oOn the south-facing slope but not the north aspect, insolation raised nest temperature, thereby increasing feeding activity. Prolonged temperature drops below the feeding thresholds occurred at all sites during the coldest months, leading to starvation and partial mortality. Nonetheless, even the more most extreme (colder) sites still allowed some feeding, and, consequently, up to 20% colony survival and successful pupation. Given that the present distribution of the oligophagous T. pityocampa is not constrained by the distribution of its actual or potential hosts, and that warmer winters will cause the number of hours of feeding to increase and the probability of the lower lethal temperature to decrease, we expect the trend of improved survival in previously prohibitive environments to continue, causing further latitudinal and altitudinal expansion. This work highlights the need to develop temperature-based predictive models for future range shifts of winter-limited species, with potential applications in management.