Abstract
Spotted wing drosophila, Drosophila suzukii Matsumura, is a major pest of small fruit worldwide in temperate and subtropical growing regions. In Northern climates, D. suzukii likely overwinters locally under leaf litter and snow pack, but our understanding of the factors affecting thermal susceptibility is limited. While previous investigations of thermal susceptibility in this species have employed conventional static acclimation protocols, we aimed to determine whether gradual cooling, or dynamic acclimation, may extend the limits of known thermal tolerance by more closely approximating naturally occurring shifts in temperature. First, we assessed survival among adult and pupal D. suzukii using static acclimation. Then, we re-assessed survival using a novel dynamic acclimation method. We found that while static acclimation was sufficient to induce cold tolerance, dynamic acclimation significantly improved survival at temperatures as low as −7.5 °C. Following static acclimation, the lower lethal limit of adult D. suzukii was −1.1 °C in winter morphotype (WM) adults compared to 1.7 °C in non-acclimated summer morphotype (SM) adults. Dynamic acclimation reduced the lower limit to −5 °C in SM flies. At the end of our study 50% of WM flies survived 72 h at −7.5 °C. Below 0 °C pupal survival declined significantly regardless of acclimation procedure. However, pupal acclimation improved survival outcomes significantly compared to non-acclimated pupae, suggesting that while juvenile diapause is unlikely, cold hardening likely benefits those flies which may develop into the overwintering WM population. These data suggest that the degree of cold hardening is proportional to the thermal environment, a finding previously unrecognized in this species. Given the economic impact of this pest, these data may have important implications for offseason population monitoring and management. We discuss how phenotypic plasticity may drive geographical range expansion, and the impact of climate change on the spread of this species.
Highlights
Spotted wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is a major invasive pest of small fruit crops in North America, South America, and Europe [1,2,3,4], with potential to spread to Africa and Oceania [4]
D. suzukii in response to acute andtemperatures sustained(WM
We foundadult that long-term developmental exposure to cool significantly improved in adult D. suzukii in response to 64.4, acute and cold exposure, compared to cold-acclimated andsurvival non-acclimated
Summary
Drosophila suzukii Matsumura (Diptera: Drosophilidae), is a major invasive pest of small fruit crops in North America, South America, and Europe [1,2,3,4], with potential to spread to Africa and Oceania [4]. In Northern climates, D. suzukii reaches peak populations in the summer, which coincides with warm temperatures and peak fruit abundance [5,11,12,13]. The time of first capture varies yearly and regionally, and is presumably affected by the degree and duration of extreme cold temperatures to which the insects were exposed the previous winter. The behavioral and physiological mechanisms by which this relatively cold-intolerant insect [20,21,22] survives harsh winters remains unclear
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