Wolbachia improves the performance of an invasive fly after a diet shift

Polyphagy is an adaptative strategy allowing species to develop and survive on multiple diets. Phytophagous insects can be exposed to sub-optimal resources, as host plants vary in nutritional quality. Some insects may rely on symbiotic bacteria to better utilize less favorable substrates. The invasive fruit fly Drosophila suzukii is a highly successful pest worldwide. The use of ripening and ripe fruits, a niche neglected by other drosophilids, and its polyphagy may have contributed to its global spread. The role of D. suzukii 's Wolbachia strain ( w Suz) remains unconfirmed, although a mutualistic role has been hypothesized via virus protection or dealing with abiotic stress. In some insect species, Wolbachia acts as a nutritional mutualist. This study explored the role of w Suz in D. suzukii adaptation to fluctuating diet regimes. To simulate a diet shift, we used Wolbachia -infected and uninfected flies, maintained on a corn-based (low-starch) or a grape-based (high-starch) diet for at least 10 generations. Then, we placed individuals from each line on one or the other diet for 30 days. The effects of Wolbachia and the diet treatments were assessed by quantifying female fecundity, egg-to-adult development time and survival, and offspring mass. The presence of Wolbachia positively affected female fecundity and offspring mass after a diet shift. Wolbachia also increased survival during larval development regardless of the diet, supporting its mutualistic role. Our results underline the role of w Suz on D. suzukii diet tolerance and performance. A better understanding of the role of symbionts in invasive species could help to improve management strategies.