The assembly of the seed microbiota involves some early microbial seed colonizers that are transmitted from the maternal plant through the vascular system, while other microbes enter through the stigma. Thus, the seed microbiota consists of microbes not only recruited from the vascular tissues of the plant, but also from the flower. Flowers are known to be a hub for microbial transmission between plants and insects. This floral-insect exchange opens the possibility for insect-transmitted bacteria to colonize the ovule and subsequently the seed, and to pass then into the next plant generation. In this study, we evaluated the contribution of insect pollination to the seed microbiota through high-throughput sequencing. Oilseed rape (OSR) Brassica napus flowers were exposed to visits and pollination by honey bees (Apis mellifera) or red mason bees (Osmia bicornis), hand pollination, or autonomous self-pollination (ASP). Sequence analyses revealed that honey bee visitation reduced the bacterial richness and diversity, increased the variability in the seed microbial structure, and introduced bee-associated taxa. In contrast, mason bee pollination had minor effects on the seed microbiota. We highlight the need to consider insect pollination as an ecological process involved in the transmission of bacteria from flower to seeds.