On the overwintering ability of Drosophila suzukii in South Tyrol

BACKGROUND: Drosophila suzukii became one of the most dangerous pests in fruit crops and vineyards in Europe since 2009. Lacking knowledge of the overwintering biology under European environmental conditions makes an environmentally friendly control of this invasive pest difficult. OBJECTIVE: The objective of this study was to investigate its hibernation capability under the climatic conditions of South Tyrol, Italy. METHODS: Monitoring flight activity by baited traps revealed an overwintering location in the Adige valley. We determined the reproductive status of females trapped weekly at Schlossleiten from August 2012 until September 2013 by dissecting their abdomens. For further potential correlation between overwintering locations, reproductive status, and climatic conditions were assessed. RESULTS: The microclimatic conditions of single locations affected overwintering success and suggest the aggregation of adults in most favourable hibernation sites where a high proportion of females is able to survive. However, in spring some of the females showed degenerated reproductive organs. Dissection of abdomens evinced a reproductive diapause, which appears to be affected by winter climatic conditions, the nutritional status, and food availability. CONCLUSIONS: D. suzukii is able to overwinter in the South Tyrolean area. Control and management of the potential hibernation sites may delay the population dynamics in the following season.