About the overwintering ability of Drosophila suzukii in South Tyrol

Abstract: As D. suzukii is known to be thermo sensitive, we investigated its ability to overwinter in the climatic conditions of the South Tyrolean area. The monitoring of the fly activity using Droski-drink baited traps allowed to detect an overwintering locality in the Adige valley at 300 m a.s.l. We determined the reproductive condition of all females trapped weekly in the period from August 2012 until September 2013 by dissecting their abdomen. In order to find a correlation between overwintering localities, reproductive status and climatic conditions, microclimatic data (air temperature and RH at 50-100 cm ground level, and temperature under the forest mulch) were registered. The results showed that the microclimatic conditions of single localities are of great impact for the overwintering and suggest that the adults aggregate in most favourable overwintering sites. In such sites a high part of the female population is able to survive, however in spring some of them show degenerated reproductive organs. Dissection of abdomens revealed a reproductive diapause in winter, which appears to be affected by the winter climatic conditions, the nutritional status and food availability.