Why are there so many species of mining bees (Hymenoptera, Andrenidae)? The possible roles of phenology and <i>Wolbachia</i> incompatibility in maintaining species boundaries in the <i>Andrena proxima</i> ‐complex

The factors leading to the extraordinary diversity of bees genus Andrena Fabricius, second most speciose among bees, remain largely unknown. To examine pattern diversification in this genus, we investigate species boundaries within controversial proxima-complex using a dataset ultra-conserved elements and various delimitation analyses (admixture analyses, BPP, DAPC). Our results confirm presence three separate group (Andrena proxima (Kirby), A. ampla Warncke alutacea Stöckhert) suggest very low levels interspecific gene flow. are regularly found sympatry, suggesting an advanced stage speciation. By contrast, shows parapatric distribution with both other species. harbours unique strain Wolbachia Hertig, absent two species, which infected by same strains Wolbachia. In addition, have distinct phenologies, flying earlier season significantly later; phenology is intermediate. that Wolbachia-induced incompatibilities phenological differences maintain group. speciation observed showing putatively incompatible strongly proxima. We propose smaller differentiation between may explain distribution. discuss how these underlie high rate groups Andrena, characterized particularly variable short periods.