Developmental Acclimation of Drosophila suzukii (Diptera: Drosophilidae) and Its Effect on Diapause and Winter Stress Tolerance.

We investigated the influence of developmental conditions on adult morphology, reproductive arrest, and winter stress tolerance of the invasive pest of small fruit, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). Cooler rearing temperatures (15 °C) resulted in larger, darker "winter morph" (WM) adults than "summer morph" flies reared at optimal temperatures (25 °C). Abdominal pigmentation scores and body size measurements of laboratory-reared WMs were similar to those of D. suzukii females captured in late autumn in Geneva, NY. We evaluated reproductive diapause and cold hardiness in live-captured D. suzukii WMs as well as WMs reared in the laboratory from egg to adult under four developmental conditions: static cool temperatures (SWM; 15 °C, 12:12 h L:D), fluctuating temperatures (FWM; 20 °C L: 10 °C D, 12:12 h L:D), and static cool temperatures (15 °C, 12:12 h L:D) followed by posteclosion chilling (CWM; 10 °C) under short-day (SD; 12:12 h L:D) or long-day photoperiods (LD; 16:8 h L:D). Live-captured D. suzukii WMs and CWMs had longer preoviposition times than newly eclosed summer morph adults, indicating a reproductive diapause that was not observed in SWMs or FWMs. Additionally, recovery after acute freeze stress was not different between CWM-SD females and live captured WM females. More 7-d-old CWMs survived 0, -1, or - 3 °C freeze stress than summer morph adults, and more CWM-SD adults survived -3 °C freeze stress than CWM-LD adults. Survival after -3 °C freeze stress was significantly higher in diapausing, CWMs than nondiapausing SWMs and FWMs.

Wallingford AK ，Loeb GM 《-》

Reproductive arrest and stress resistance in winter-acclimated Drosophila suzukii.

Overwintering insects must survive the multiple-stress environment of winter, which includes low temperatures, reduced food and water availability, and cold-active pathogens. Many insects overwinter in diapause, a developmental arrest associated with high stress tolerance. Drosophila suzukii (Diptera: Drosophilidae), spotted wing drosophila, is an invasive agricultural pest worldwide. Its ability to overwinter and therefore establish in temperate regions could have severe implications for fruit crop industries. We demonstrate here that laboratory populations of Canadian D. suzukii larvae reared under short-day, low temperature, conditions develop into dark 'winter morph' adults similar to those reported globally from field captures, and observed by us in southern Ontario, Canada. These winter-acclimated adults have delayed reproductive maturity, enhanced cold tolerance, and can remain active at low temperatures, although they do not have the increased desiccation tolerance or survival of fungal pathogen challenges that might be expected from a more heavily melanised cuticle. Winter-acclimated female D. suzukii have underdeveloped ovaries and altered transcript levels of several genes associated with reproduction and stress. While superficially indicative of reproductive diapause, the delayed reproductive maturity of winter-acclimated D. suzukii appears to be temperature-dependent, not regulated by photoperiod, and is thus unlikely to be 'true' diapause. The traits of this 'winter morph', however, likely facilitate overwintering in southern Canada, and have probably contributed to the global success of this fly as an invasive species.

Toxopeus J ，Jakobs R ，Ferguson LV ，Gariepy TD ，Sinclair BJ ... -  《-》

Cold Hardiness of Winter-Acclimated Drosophila suzukii (Diptera: Drosophilidae) Adults.

Drosophila suzukii Matsumura, often called spotted wing drosophila, is an exotic vinegar fly that is native to Southeast Asia and was first detected in the continental United States in 2008. Previous modeling studies have suggested that D. suzukii might not survive in portions of the northern United States or southern Canada due to the effects of cold. As a result, we measured two aspects of insect cold tolerance, the supercooling point and lower lethal temperature, for D. suzukii summer-morph pupae and adults and winter-morph adults. Supercooling points were compared to adults of Drosophila melanogaster Meigen. The lower lethal temperature of D. suzukii winter-morph adults was significantly colder than that for D. suzukii summer-morph adults, while supercooling points of D. suzukii winter-morph adults were actually warmer than that for D. suzukii summer-morph adults and pupae. D. suzukii summer-morph adult supercooling points were not significantly different than those for D. melanogaster adults. These measures indicate that D. suzukii is a chill intolerant insect, and winter-morph adults are the most cold-tolerant life stage. These results can be used to improve predictions of where D. suzukii might be able to establish overwintering populations and cause extensive damage to spring fruit crops.

Stephens AR ，Asplen MK ，Hutchison WD ，Venette RC ... -  《-》

Seasonal cues induce phenotypic plasticity of Drosophila suzukii to enhance winter survival.

Shearer PW ，West JD ，Walton VM ，Brown PH ，Svetec N ，Chiu JC ... -  《BMC ECOLOGY》

Adult plasticity of cold tolerance in a continental-temperate population of Drosophila suzukii.

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is a worldwide emerging pest of soft fruits, but its cold tolerance has not been thoroughly explored. We determined the cold tolerance strategy, low temperature thermal limits, and plasticity of cold tolerance in both male and female adult D. suzukii. We reared flies under common conditions (long days, 21°C; control) and induced plasticity by rapid cold-hardening (RCH, 1h at 0°C followed by 1h recovery), cold acclimation (CA, 5 days at 6°C) or acclimation under fluctuating temperatures (FA). D. suzukii had supercooling points (SCPs) between -16 and -23°C, and were chill-susceptible. 80% of control flies were killed after 1h at -7.2°C (males) or -7.5°C (females); CA and FA improved survival of this temperature in both sexes, but RCH did not. 80% of control flies were killed after 70 h (male) or 92 h (female) at 0°C, and FA shifted this to 112 h (males) and 165 h (females). FA flies entered chill coma (CTmin) at approximately -1.7°C, which was ca. 0.5°C colder than control flies; RCH and CA increased the CTmin compared to controls. Control and RCH flies exposed to 0°C for 8h took 30-40 min to recover movement, but this was reduced to <10 min in CA and FA. Flies placed outside in a field cage in London, Ontario, were all killed by a transient cold snap in December. We conclude that adult phenotypic plasticity is not sufficient to allow D. suzukii to overwinter in temperate habitats, and suggest that flies could overwinter in association with built structures, or that there may be additional cold tolerance imparted by developmental plasticity.

Jakobs R ，Gariepy TD ，Sinclair BJ 《-》