Stage-Specific and Seasonal Induction of the Overwintering Morph of Spotted Wing Drosophila (Diptera: Drosophilidae)

Abstract

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is currently a major pest management challenge in berry and cherry production. This species has a winter morph phenotype with longer wings and increased melanization associated with survival in colder conditions. Measurements of wing morphology in Michigan D. suzukii collected during 2016 and 2017 showed that induction of this morph began in September and increased into December, correlated with decreasing temperature and day length. Importantly, we found that wing length increases along a continuous scale and there is overlap between the two morph types. We tested whether temperature or photoperiod elicited this phenotypic change using a factorial design with each preadult lifestage held at 10 or 25°C and 16:8 or 8:16 L:D. Our results support temperature as the main driver of transition to the winter morph for all immature stages. Comparing the reproductive capacity of winter morph flies in cold conditions and when previously acclimated to warm conditions, flies with the acclimation experience laid comparable numbers of eggs as the summer morphs at 25°C, indicating that winter morphs can reproduce after surviving cold periods. These results highlight the ability of D. suzukii to adapt to changing temperature conditions, allowing it to survive cold and also exploit warmer periods to build populations when conditions allow.

Seasonal morphotypes of Drosophila suzukii differ in key life‐history traits during and after a prolonged period of cold exposure

“…Although the striking phenotypic differences between SM and WM of D. suzukii affect their individual performances under prevailing conditions, they may also have an impact on their seasonal population dynamics. Individuals of both seasonal morphotypes co‐occur in autumn and in spring (Leach, Stone, Van Timmeren, & Isaacs, 2019; Panel et al., 2018; Shearer et al., 2016), but they are expected to have different life‐history strategies, in particular regarding the investment in reproduction and survival. For instance, WM flies can better survive prolonged cold exposure and lower temperatures than SM flies (Shearer et al., 2016; Stephens et al., 2015; Stockton, Wallingford, & Loeb, 2018; Toxopeus et al., 2016).…”

Late seasonal occurrence of the spotted wing pest in new invaded area

“…Interestingly, all individuals were recorded only in autumn. The flying activity of D. suzukii is reported throughout the year in their natural, but also invasive range, where it has been present for a longer time (see Asplen et al 2015, Arnó et al 2016, Rossi-Stacconi et al 2016, Leach et al 2019. In North-eastern Slovakia, directly adjacent to the region where our new D. suzukii occurrences were confirmed, the species was also caught only in autumn (Oboňa et al 2017).…”

“…Generations hatched throughout the warm season have shorter lifespans than generations hatched after September. Only adults (the winter morph) overwinter successfully as was found out by Lee et al (2011), Asplen et al (2015), Leach et al (2019), etc. In Ukraine, similarly to Slovakia (Oboňa et al 2017), captured specimens represented only summer forms, the winter morph (see Leach et al 2019) was absent.…”

“…Only adults (the winter morph) overwinter successfully as was found out by Lee et al (2011), Asplen et al (2015), Leach et al (2019), etc. In Ukraine, similarly to Slovakia (Oboňa et al 2017), captured specimens represented only summer forms, the winter morph (see Leach et al 2019) was absent. According to Harris et al (2014), in California (USA), this pest has two distinct periods of trap capture: in spring (which has not been confirmed in Ukraine) despite the sampling, and through mid-summer.…”

Risk of Spotted-Wing Drosophila Injury and Associated Increases in Acetic Acid in Minnesota Winegrapes

“…However, temperatures during the time interval of each trial varied tremendously and may have had an impact on the results by limiting D. suzukii activity. Previous studies have indicated temperatures below 10°C will arrest movement and development of D. suzukii (Ryan et al 2016, Leach et al 2019. In 2019, the late-season trials experienced an average temperature of 8°C, which falls below the 10°C threshold for D. suzukii.…”