Multiple lines of evidence for reproductive winter diapause in the invasive pest Drosophila suzukii: useful clues for control strategies

Successful management of invasive pests, such as Drosophila suzukii, relies on a fine understanding of their biology. Genomic and physiological studies have suggested that the invasive success of D. suzukii is strongly associated with its ability to overwinter in a reproductive diapause state. Here, we coupled field surveys with comparative morphology and genetics to increase our understanding of D. suzukii overwintering behavior and provide useful indications for its management. The results of a 4-year-long field trapping in an Italian mountain region indicate that D. suzukii is continuously captured during winter months and that the number of captures is correlated with temperature. Capture patterns are also contrasting between sexes: while females are more abundantly caught during winter and summer, males are more abundant in spring and autumn. We found that overwintering could occur not only in natural environments, such as woods, but also in anthropic shelters. Comparative morphology and genetics further indicate that spermathecae may play an important adaptive role during winter. Our results unveil complex winter biology in D. suzukii and highlight how the number of overwintering females is an earlier predictor of summer population size. We hence propose that in a given year infestation may be better forecasted by taking into account the captures of the previous winter. We recommend that control methods be diapause-aware. For instance, they should take place in late winter/early spring and close to natural environments, and not only in fruit ripening season and close to orchards.