Transmission of yeast and bacterial symbionts between sexual partners in <i>Drosophila suzukii</i> and <i>Drosophila melanogaster</i>

Sexually transmitted symbionts can substantially affect the performance and evolution of their hosts. From a pest control perspective, the sexually transmitted microorganisms of insects can be considered powerful biological control agents or probiotics. The sterile insect technique (SIT) is currently being developed as a new tool to control <i>Drosophila suzukii</i>, a major crop pest. With considerable numbers of mass-reared insects released to mate with wild individuals, understanding how microbiota transfers between adult insects is necessary not only to improve the effectiveness of the technique but also to prevent the potential spread of non-native and harmful microorganisms in wild arthropod populations and their environment. We investigated the sexual transmission of yeast and bacterial symbionts in <i>Drosophila suzukii</i> and in the universal model <i>Drosophila melanogaster</i>. In an ecologically realistic set-up, we combined behavioural and microbiological measurements using flies associated with four microorganisms. We detected microbial transmission more frequently in mated flies, which was mostly influenced by the identity and density of microbial strains in the donor and recipient hosts. Our results suggest the importance of using hosts associated with several microorganisms in microbiota transmission studies, open new perspectives for crop protection and point to an overlooked non-target effect of the SIT.