Reassessment of Horstia and Related Mites Reveals Multiple Origins of Bee Association and Supports Recognition of Two Families, Horstiidae and Cerophagidae (Acari: Astigmata), with Establishment of Phloeohorstia gen. nov.

This study re-evaluates the evolutionary relationships of Horstia and allied bee-associated astigmatid mites using an integrative framework combining morphological reassessment and previously generated molecular phylogenetic evidence. Our results fundamentally challenge the long-standing hypothesis that bee associations in these mites and related mites, formerly placed in “Horstiinae”, originated once from a common bee-associated ancestor. Instead, the data support multiple independent origins of bee-associated lifestyles and justify the recognition of two distinct families, Horstiidae and Cerophagidae. These findings further demonstrate the limitations of relying on host association as a primary taxonomic character in Astigmata. In the present case, bee-associated taxa are distributed among multiple unrelated lineages, consistent with repeated host colonization and ecological fitting rather than inheritance from a single bee-associated ancestor. Bee nests represent nutrient-rich and spatially discrete habitats that were repeatedly invaded by preadapted mite lineages capable of exploiting stored organic materials. At the same time, both Horstiidae and Cerophagidae exhibit strong host conservatism once established, suggesting that transitions into bee nests are evolutionarily rare but stable over long timescales. The presence of free-living species retaining plesiomorphic morphological traits further supports a free-living ancestral condition in Horstia, with bee association representing a secondary ecological transition. For the free-living species formerly placed in Horstia we propose a new genus, Phloeohorstia gen. nov. and describe Phloeohorstia corticalis sp. nov. based on both adults and heteromorphic deutonymphs. Together, our results provide a more natural classification framework for these mites and highlight the need to re-evaluate other host-associated groups within Astigmata using integrative phylogenetic approaches.