primarily kleptoparasitic when feed on pollen but can be neutral to beneficial when feed on fungus in bee nests
Adult: Only one solendion σ on genu I (Fig. 9).
Phoretic deutonymph: Propodosomal shield transversely striated, hysterosomal shield with longitudinal and transverse striations (striate pattern may be faint) (Fig. 1). External vertical setae ve represented by vestigial alveoli (Fig. 3). Supracoxal setae scx absent (Fig. 3). Coxal setae 1a, 3a, 4b alveolar; in contrast, coxal setae 4a in the form of large, striate conoids (Figs. 2, 4). Setae aa I, and ba I-II absent (Figs. 3). Solenidion ω2 absent from tarsus I, represented by vestigial alveolus (Fig. 3). Solenidion σ III and seta nG III absent from genu III (Fig. 4). Tarsus IV with 1 seta (d IV) longer than leg IV (Fig. 4).
Adult: External vertical setae (ve) represented by alveoli, located on lateral sides of prodorsal shield, approximately midway between vi and scapular setae se (Fig. 9). Hysterosomal setae c1, c2, d1, and f2 present (Figs. 5, 7, 8; notice that f2 is very short and may not be easily seen in female). Grandjean's organ biramous (Fig. 8) and setae ba I-II absent (Fig. 9). Male with sclerotized projection extending from posterior opisthosoma (Figs. 7, 8). Projection is broad, with setae h2 and h3 dorsally and setae ps1, ps2, and f2 ventrally (Figs. 7, 8).
A dichotomous key is available in Ochoa and OConnor, 2000.
Ground-nesting apid bees of the genus Epicharis, subgenera Triepicharis, Parepicharis, Hoplepicharis, Epicharis (s.str.), and Epicharana. Epicharis subgenera Epicharoides and Epicharitides lack these mites.
associated exclusively with bees or their close relative, wasps; cannot live without these hosts
some life stages are associated with bees, while others are not
can complete entire life cycle without bees or their close relative, wasps
Species of Horstiella are exclusively associated with the ground-nesting bee genus Epicharis in the Neotropics (Figs. 13-19). This association is quite unusual in that most species of Epicharis harbor two species of Horstiella, a condition known as synhospitality (Ochoa and OConnor, 2000) (Figs. 14, 16); the mite species pairs were almost always spatially segregated on an individual host (Fig. 14).
Most Horstiella species are commonly found on the bee's mesosoma and 1st metasoma tergite, though Horstiella megamyzidos specifically attaches under the lateral edges of the metasomal tergites (Fig. 14) and under the sternites. In male bees, the more frequent mite attachment site is the ventral region of the mesosoma and metasoma (Fig. 18), which correlates with the mating position of the host bees. Because only the female bee makes nests, mites developing in a cell with a male bee would normally have no opportunity to found new colonies. Migrating to the ventral surface of male bees would, therefore, give the mites a selective advantage because this can facilitate transfer onto the body of a female bee during copulation, which occurs with the male above the female (Ochoa and OConnor, 2000).
Large quantities of pollen grains as well as fungal conidia were found in guts of adult mites found in nests of Epicharis rustica (Figs. 11, 12; our data, unpublished). These observations suggest that the mites are primarily kleptoparasitic pollen-feeders but can also be fungivorous in bee nests.