Ovary Development and Cold Tolerance of the Invasive Pest Drosophila suzukii (Matsumura) in the Central Plains of Kansas, United States

Abstract

Environmental challenges presented by temperature variation can be overcome through phenotypic plasticity in small invasive ectotherms. We tested the effect of thermal exposure to 21, 18, and 11°C throughout the whole life cycle of individuals, thermal exposure of adults reared at 25°C to 15 and 11°C for a 21-d period, and long (14:10 hr) and short (10:14 hr) photoperiod on ovary size and development in Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) cultured from a recently established population in Topeka, Kansas (United States). Examination of the response to temperature and photoperiod variation in this central plains population provides insight into the role of phenotypic plasticity in a climate that is warmer than regions in North America where D. suzukii was initially established. We found both low temperature and short photoperiod resulted in reduced ovary size and level of development. In particular, reduced ovary development was observed following exposure to 15°C, indicating that ovary development in females from the central plains population is more sensitive to lower temperature compared with populations examined from the northern United States and southern Canada. We also provide evidence that D. suzukii reared at 25°C are capable of short-term hardening when exposed to -6°C following 4°C acclimation, contrary to previous reports indicating flies reared at warm temperatures do not rapidly-cold harden. Our study highlights the central role of phenotypic plasticity in response to winter-like laboratory conditions and provides an important geographic comparison to previously published assessments of ovary development and short-term hardening survival response for D. suzukii collected in cooler climates.

Cold acclimation triggers lipidomic and metabolic adjustments in the spotted wing drosophilaDrosophila suzukii(Matsumara)

“…1). The basal cold survival of control flies measured after exposure to Ϫ5°C for 100 min was similar to data reported by Jakobs et al (45), and Everman et al (28), (i.e., 20% survival after 1 h at Ϫ7°C and 10% after 1 h at Ϫ6°C, respectively), and cold acclimation greatly promoted acute cold stress survival, as previously reported (105). Shorter CCRT after adult acclimation has also been reported by Jakobs et al (45).…”

“…These winter flies probably resulted from larvae and pupae that developed in fruits in autumn (50). Hence, they may acclimate during both development and as adult (28,84,90,93,101,105). Therefore, it is likely that wild D. suzukii can use physiological adjustments similar to the ones we described here to enhance their cold tolerance and successfully overwinter in invaded areas.…”

“…The overwintering success of D. suzukii likely relies on two main strategies: 1) migration to favorable and buffered microhabitats, such as forests; indeed, underneath the forest mulch temperatures remain positive in winter (89,111); and 2) acquisition of cold tolerance via plastic responses (90). Several studies have shown that this fly is able to enhance its cold tolerance thanks to various cold acclimation types, such as rapid cold hardening (28,101), adult gradual acclimation (45,104), or developmental acclimation (90,101,105). Recently, cold-acclimated D. suzukii flies have been shown to survive temperatures as cold as Ϫ7.5°C (94).…”

Cold Acclimation Favors Metabolic Stability in Drosophila suzukii

“… Everman et al (2018) found a similar rapid cold-hardening response in non-acclimated flies exposed at 4°C for 2 h. This fly is also capable of acquiring cold tolerance via acclimation at adult stage ( Jakobs et al, 2015 ; Wallingford and Loeb, 2016 ), or via developmental acclimation ( Toxopeus et al, 2016 ; Wallingford and Loeb, 2016 ). In D. suzukii , developmental acclimation at temperatures below 12°C (combined or not with short photoperiod) results in a phenotype showing increased body size, dark pigmentation, reproductive arrest, and enhanced cold tolerance; this phenotype, referred to as “winter morph”, is supposed to be the overwintering form of D. suzukii ( Stephens et al, 2015 ; Shearer et al, 2016 ; Toxopeus et al, 2016 ; Wallingford and Loeb, 2016 ; Everman et al, 2018 ). Effect of the different forms of acclimation on subsequent cold tolerance has been rather well described in D. suzukii , but surprisingly, the mechanisms underlying cold tolerance acquisition through acclimation in this species are still poorly understood.…”

Phenology of Drosophila species across a temperate growing season and implications for behavior

“…Low temperature tolerance changes with morphology as those with a dark morphology have a lower temp resistance than light morphs [75]. The dark morph is induced by low temperatures, independent of day length, and is accompanied by increased body size and reproductive quiescence, which likely collectively contribute to increased thermal stress resistance [76–79].…”