Drosophila suzukii (Matsumura, 1931), the spotted-wing drosophila, is a highly invasive fruit fly that spread from Southern Asia across most regions of Asia, and in the last fifteen years has invaded Europe and the Americas. It is an economically important pest of small fruits such as berries and stone fruits. Drosophila suzukii speciated by adapting to cooler, mountainous and forest environments. In temperate regions, it evolved seasonal polyphenism traits which enhanced its survival during stressful winter population bottlenecks. Consequently, in these temperate regions, the populations undergo seasonal reproductive dynamics. Despite its economic importance, no data are available on the behavioural reproductive strategies of this fly. The presence of polyandry, for example, has not been determined despite the important role it might play in the reproductive dynamics of the populations.

We explored the presence of polyandry in an established population in Trentino, a region in North Italy. In this area, D. suzukii overcomes the winter bottleneck and undergoes a seasonal reproductive fluctuation. We observed a high remating frequency in females during the late spring demographic explosion that led to the abundant summer population. The presence of a high degree of polyandry and shared paternity associated with the post-winter population increase raises the question of the possible evolutionary adaptive role of this reproductive behaviour in D. suzukii.

Multilocus genotyping was performed using four dinucleotide repeat microsatellite loci: DS05, DS09, DS15 and DS22 chosen from the previously characterized SSR sequences (Fraimount et al., 2015). Genotypes were determined for each mother and her progeny.

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