Development of Drosophila suzukii at low temperatures in mountain areas

As a fly tracking the availability of fruits along climatic gradients, Drosophila suzukii is deemed to be rather flexible in relation to environmental factors, among which temperature is a major player. We sampled potential wild host fruits of D. suzukii along two elevational gradients in mountain areas of north-eastern Italy, in order to measure fly performance in relation to temperature. In addition, we used a strong natural temperature gradient in an open-top cave, covering the lower range of temperatures known for D. suzukii, to deploy laboratory stock colonies to mimic conditions existing along elevational gradients. At least nine wild host species yielded adults of D. suzukii in the mountain area (Daphne mezereum, Lonicera alpigena,Lonicera caerulea, Lonicera nigra, Lonicera xylosteum, Rubus caesius, Rubus saxatilis, Sambucus nigra, and Sambucus racemosa) when the daily average temperature in the three preceding weeks was at least 11.1 °C. Similar results were obtained with the laboratory colonies reared on an artificial medium in the cave, where oviposition and development from egg to adult occurred at above 11.6 °C. Both values are lower than previously recorded lower thresholds for development at both constant and fluctuating temperatures. These findings indicate that D. suzukii performs well at low temperatures, suggesting that population buildup may occur even under these conditions, with likely consequences on crops and wild host reproduction.