The interactions of Sennertia with their hosts in nests remain largely unknown. There are conflicting accounts suggesting either negative or neutral effect of the mite presence. In the former case, the damage to developing bees was marginal and always substantially less than that of Chaetodactylus.
Feeding stages of the Sennertia vaga-group are unusual because they can disperse on adult bees of the genera Centris (Paracentris) and Xylocopa (Fig. 8). Reproduction and feeding can also occur during dispersal. Species of the Sennertia vaga group probably do not form phoretic deutonymphs and disperse exclusively as feeding stages. Observations on these mites inside nests are lacking.
Phoretic deutonymphs (non-feeding stages, Figs. 1-7) disperse on adult bees from one nest to another (Figs. 9-13). Ceratina bees associated with Sennertia (S. sayutara and S. devincta) have acarinaria, indirectly suggesting mutualistic relationship between the mites and the bees (Fig. 14). Some other bees have rudimentary acarinaria that their mites take advantage of for phoresy. Sennertia koptorthosomae and S. hipposideros, which are associated with Asian large carpenter bees (Xylocopa), have special pouches filled with fungal spores (sporothecae) on the hysterosoma (Klimov and OConnor, 2008) (Fig. 15), suggesting that they may transfer fungi from one bee nest to another. It is unknown whether these fungi can cause harm to the bee host.
Sennertia cerambycina (Fig. 2) is normally associated with Xylocopa, feeding on the provisioned pollen in the bee nest. Rarely, dead bee eggs and larvae can be found in the infested cells. However, it is unclear if the mite directly or indirectly causes death of eggs or larvae (Vicidomini, 1996). Adult bees of Xylocopa violacea extensively infested with S. cerambycina show slow flight, lack of precision in flying trajectories, difficult and imprecise landing, heavy take-off, and reduced feeding rates (Vicidomini, 1999).
Duchemin (1886) reported the death of 30 honey bee (Apis mellifera) hives in France attributable to a mite identified originally as Sennertia cerambycina. The mite infests honey bees visiting sunflowers, eventually causing death of colonies. Similar cases (e.g., death of honey bee colonies with the introduction of sunflowers) were reported in Russia at the end of 19th to the beginning of the 20th century (reviewed in Grobov, 1978). Experimental data suggesting that the mite is responsible for the death of bees are, however, absent. Furthermore, misidentification is possible here and it may be that another mite species, not belonging to the genus Sennertia, was involved in these cases.