|LOEB, GREGORY - Cornell University
Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2021
Publication Date: 4/28/2021
Citation: Stockton, D.G., Loeb, G.M. 2021. Winter warm-up frequency and the degree of temperature fluctuations affect survival outcomes of winter morphotype Drosophila suzukii (Diptera: Drosophilidae). Journal of Insect Physiology. 131:104246. https://doi.org/10.1016/j.jinsphys.2021.104246.
Interpretive Summary: Spotted-wing drosophila is a major overwintering invasive pest found along the U.S. East coast and Great Lakes region of the American Midwest. Detection of this pest, and models that forecast pest pressure from year to year, rely on accurate survival threshold estimates, which our previous research suggests are often underestimated due to oversimplification of the modes of acclimation often used during cold tolerance assessments. For that reason, we examined the role of temperature fluctuations on Spotted-wing survival and we attempted to better understand the environmental conditions that constrain or promote the establishment and further spread of this pest. Our results showed that thermal stability has differential effects depending on the temperature range in question and the degree of acute cold shock to which in the insects are exposed. When temperatures were near freezing, daily warm up periods improved survival over the long term. The primary implication of this work is that these types of nuanced assessments of thermal thresholds of survival are key for accurately predicting population dynamics of this invasive pest. We hope to incorporate these data into existing modeling networks and improve our understanding of the factors contributing to pest pressure changes from year to year.
Technical Abstract: Among overwintering Drosophila suzukii, discrete environmental changes in temperature and photoperiod induce a suite of biochemical changes conferring cold tolerance. However, little is known regarding how temperature fluctuations, which can influence metabolic and cellular repair activity, affect survival outcomes in this species. For that reason, we designed three experiments to test the effects of intermittent warm-up periods and the degree of temperature fluctuation on winter morphotype (WM) D. suzukii survival. We found that at 5 °C, a temperature sufficient to induce reproductive diapause, but warm enough to allow foraging, increasing warm-up frequency (warmed to 25 °C at various interval schedules) was associated with decreased survival. In contrast, when the nightly low temperature was 0 °C, daily fluctuations that warmed the environment to temperatures above freezing (5, or 15 °C) appeared beneficial and resulted in improved survival compared to flies held at 0 °C during day and night. When we next evaluated cold tolerance using a 24-hour stress test assay (-5 °C), we found that again, thermal fluctuations improved survival compared to static freezing conditions. However, we also found that WM D. suzukii exposed to freezing temperatures during acclimation were less cold tolerant, regardless of the thermal fluctuation schedule, indicating that there may be tradeoffs between adequate acclimation temperature, which is required to induce cold tolerance, and the ensuing effects of incidental chill injury. Moving forward, these data, which account for the nuanced interactions between the thermal environment and in the internal physiology of D. suzukii, may help refine seasonal populations models, which aim to forecast pest pressure based on conditions the previous winter.