Field-acclimated Drosophila suzukii (Diptera: Drosophilidae) from the Saguenay–Lac-Saint-Jean region, Québec, Canada, were examined over two years for winter survival, under the hypothesis that flies select protected overwintering microhabitats. In 2016–2017, flies trapped alive in the field or emerged from infested fruits were submitted to four winter regimes of either constant or daily fluctuating temperatures of 5 °C (2–8 °C) or 10 °C (7–13 °C). In 2017–2018, two fluctuating regimes averaging either 1 °C (–2 to 4 °C) or 3 °C (0–6 °C) were tested. Survival was modelled using Cox proportional hazard models testing probability that mortality risk varies with cold winter regime, fly sex, and fly provenance. Hazard ratios were about 1.7 times higher for males than for females. Models indicate that flies in constant and fluctuating 10 °C, in constant 5 °C, or in fluctuating 1 °C with daily exposure to –2 °C would not survive a six-month winter. Female survival extended to the next summer in fluctuating regimes averaging 5 °C or 3 °C. Estimates of 0.95 quantile survival (5%) indicate that overwintering D. suzukii experiencing such cold temperature regimes during winter, with no prolonged sub-zero temperatures, could survive until July of the following year, which is likely at the high population densities observed.

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), the spotted-wing drosophila, is an invasive pest of fruit crops, which appeared in eastern Canada in 2010. It represents a major threat to lowbush blueberry (Vaccinium angustifolium Aiton; Ericaceae) in the Saguenay-Lac-Saint-Jean region, Québec, Canada, at the northern limits of its distribution. The dynamics, overwintering capacity, population fluctuations, and damage to lowbush blueberry of D. suzukii are unknown in Saguenay-Lac-Saint-Jean. We aimed to 1) document D. suzukii abundance and phenology in lowbush blueberry in separate localities; 2) evaluate the potential of D. suzukii to overwinter and examine population dynamics over three seasons; and 3) study the spatial distribution of D. suzukii in lowbush blueberry fields with respect to forested borders. Drosophila suzukii is abundant in lowbush blueberry fields of Saguenay-Lac-Saint-Jean. In spring, D. suzukii were absent until late June, when few summer-morph females appeared. Drosophila suzukii densities started to increase regularly in August, with increasing male proportions, to culminate in fall at high levels with balanced sex ratios. Overwintering remains uncertain, D. suzukii being undetectable in spring despite intensive trapping. Appearance of diapausing winter morphs at high densities indicates that D. suzukii responds appropriately to local conditions preceding cold winter. Models of variation of D. suzukii densities and lowbush blueberry fruit infestation with distance from borders indicate that forest borders are favoured habitats over lowbush blueberry fields and the source of D. suzukii moving to some extent into lowbush blueberry fields.

Knowing the biology and ecology of Drosophila suzukii (Diptera: Drosophilidae) is important to predict its potential for permanent establishment in cold climatic regions. We studied the reproductive potential of postdiapause male and female flies collected in lowbush blueberry fields in late season over two years. After being submitted to a six-month cold-winter regime, survivors were exposed to a simulated springtime warming regime to monitor reproductive potential and expected population growth. Overwintered fly survivors of both sexes that were aged up to nine months after field capture reproduced successfully in spring and early summer when mated to nondiapause flies experimentally made available for mating as potential migrant colonisers from lower latitudes. Relative to control nondiapause flies, the lifetime fertility of postdiapause flies was reduced by 84% in females and 70% in males, revealing large fitness costs of reproductive diapause under cold stress. Modelling potential reproduction of overwintered flies in warming conditions using models parametrised for age-dependent fertility rate and diapause status showed that nondiapause migrant flies would be strongly advantaged over locally overwintered postdiapause flies due to precocious reproductive maturity, broader pattern of age-specific fertility, and higher lifetime fertility.

Understanding movements of Drosophila suzukii (Diptera: Drosophilidae) into berry fruit crops from wild-fruit hosts in borders of semi-natural agroecosystems, such as lowbush blueberry, is important to determining harvesting time and managing wild-fruit diversity near crops. This study aimed to inventory the wild-fruit hosts associated with lowbush blueberry (Ericaceae) production in Québec, Canada, near the limits of lowbush blueberry’s eastern North American range. We also tested the hypothesis that fruit traits of berry fruit species present in or near lowbush blueberry fields might explain field infestation levels. Flies of both sexes emerged from five wild-fruit species in 2016, to which six more species were added in 2017. The most productive wild-fruit hosts were Cornus canadensis (Cornaceae) and Aralia hispida (Araliaceae) (> 100 emerged flies/100 g of fruit) in 2016, to which Prunus pensylvanica (Rosaceae) and Rubus idaeus (Rosaceae) were added in 2017. Among nine variables considered in statistical modelling (fruit size, sugar content, and reflected colour bands) and taxonomic family (a nominal variable), none could explain field infestation levels over two years. In lab tests comparing fruits of Cornus canadensis, a common weed within fields, and lowbush blueberries, mated D. suzukii females laid twice as many eggs on blueberries, but both species were equally suitable for development.