Genus Horstiella Turk, 1948, family Acaridae

Fig. 1. Horstiella quadrata, holotype, phoretic deutonymph, ex Epicharis rustica, Guyana, BMOC 82-0124-001 Click to enlarge

Bee Mites : Acari : Acariformes : Sarcoptiformes : Acaridae

Genus Horstiella Turk, 1948

Horstiella Turk, 1948: 85 (in Glycyphagidae: Chaetodactylinae); Eickwort, 1988: 331 (report from "Euglossinae"); OConnor, 1988: 343 (records from Euglossa and Eulaema including feeding stages - misidentification for undescribed genus, see Ochoa & OConnor, 2001); Eickwort, 1994: 221 (report of 2 spp. from "Euglossinae"); OConnor, 1994: 143 (record from "Euglossinae"); OConnor, 1997: 15 (mention in Horstiinae, feeding stages unknown); Ochoa and OConnor, 2000: 713 (in Acaridae: Horstiinae; revision, phylogenetic analysis; host Epicharis; feeding stages unknown); OConnor, 2001: 78 (phylogeny and host-association of Horstiinae).

Type species Horstiella armata Turk, 1948 by original designation

Diagnosis Phoretic deutonymph (after Ochoa and OConnor, 2000). Dorsum with faint to well-developed pattern of lines, transverse on propodosoma and anterior hysterosoma, longitudinal on posterior hysterosoma. External vertical setae ve absent, represented by pair of vestigial alveoli posterolateral to internal verticals (vi). Supracoxal setae scx absent. Venter with coxal apodemes well developed, coxal fields III-IV closed; coxal fields III separated, contiguous or rarely fused medially, coxal fields IV closed. Coxal setae 1a, 3a, 4b absent, coxal setae 4a in the form of large, striate conoids. Genital papillae asymmetrical, with posterior pair more attenuate. Attachment organ with anterior and median suckers normally formed, with two pairs of striate conoids and five large cuticular suckers. Legs normally formed, tarsal setation 8-8-8-8; setae aa I, ba I-II, and nG III absent; solenidion ω₂ absent from tarsus I, represented by vestigial alveolus, solenidion σ absent from genu III. All pretarsi with hooked empodial claws arising directly from tarsal apices.
Feeding stages unknown.

Biology and host associations. Species of Horstiella are exclusively associated with the ground nesting bee genus Epicharis in the Neotropics. The mites occur on the subgenera Triepicharis, Pareipcharis, Hoplepicharis, Epicharis (s.str.), and Epicharana, while the subgenera Epicharoides and Epicharitides lack these mites. The association of Horstiella and Epicharis is quite unusual in that most species of Epicharis harbor two species of Horstiella, a condition known as synhospitaly (Ochoa and OConnor, 2000). The mite species pairs were almost always spatially segregated on an individual host. No host specificity was detected, suggesting that this association is shaped after the initial diversification of the genus Epicharis (Ochoa and OConnor, 2000).
Most of Horstiella species are commonly found on the bee's propodeum, while Horstiella megamyzidos specifically attaches under the lateral edges of the metasomal tergites and under the sternites. In male bees, the more frequent attachment of mites to the ventral region of the mesosoma and metasoma 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).
Phylogeny of Horstiella, Medeus, and Horstia based on morphology was presented by Ochoa and OConnor (2000).

Distribution (show map). Neotropical region, ranging from central Mexico through Brazil (Ochoa and OConnor, 2000).

Species included.

Key to species of Horstiella
Phoretic deutonymphs

Gnathosoma wider than long; setae h3 attenuate and elongated, filiform; conoidal coxal setae 4a smaller than conoidal setae of attachment organ ... Horstiella mourei Ochoa and OConnor, 2000

Gnathosoma longer than wide; setae h₃ linear and pointed, setiform; conoidal coxal setae 4a larger than conoidal setae of attachment organ

... 2

2(1)

Internal scapular setae (sci) present, bases of sci and sce on same transverse line, elements of posterior-median apodeme IV not fused anteriorly

... 3

Internal scapular setae (sci) absent, bases of sce located posterior to bases of sci, elements of posterior-median apodeme IV fused anteriorly

... 4

3(2)

Hysterosoma with well-developed concentric lines; bases of setae h₂ close to h₃, in approximate transverse alignment with h₃ ... Horstiella concentrica Ochoa and OConnor, 2000

Hysterosoma with few oblique and longitudinal lines between setae e₁ and h₁; bases of setae h₂ located anterolaterally to h₃ ... Horstiella variabilis Ochoa and OConnor, 2000

4(2)

Tarsus III with setae s, p and r distinctly expanded basally with a fine projection distally; posterior apodeme IV thicker than diameter of seta 4a

... 5

Tarsus III with setae s, p and r simply foliate; posterior apodeme IV thinner than diameter of seta 4a

... 6

5(4)

Anterior suckers of attachment organ small (diameter 8-13) ... Horstiella snellingi Ochoa and OConnor, 2000

Anterior suckers of attachment organ large (diameter 29-49) ... Horstiella megamyzidos Ochoa and OConnor, 2000

6(5)

Attachment organ well developed, pentagonal, with large posterior medial and lateral cuticular suckers; dorsal striations weakly developed, without chevron pattern at apex of propodosomal sclerite ... Horstiella armata Turk, 1948

Attachment organ small, subquadrate, with small posterior medial and lateral cuticular suckers; dorsal striations well developed, with chevron pattern at apex of propodosomal sclerite ... Horstiella quadrata Ochoa and OConnor, 2000

References

Eickwort, G.C., 1988. The origins of mites associated with honey bees. In: Needham, G.R., Page, R.E., Delfinado-Baker, M., Bowman, C.E. (Eds.), Africanized honey bees and bee mites. Ellis Horwood, Chichester, pp. 327-338.

Eickwort, G.C., 1994. Evolution and life-history patterns of mites associated with bees. In: Houck, M.A. (Ed.), Mites: Ecological and Evolutionary Analyses of Life-History Patterns. Chapman & Hall, New York, pp. 218-251.

Ochoa, R., OConnor, B.M., 2000. Revision of the genus Horstiella (Acari: Acaridae): mites associated with Neotropical Epicharis bees (Hymenoptera: Apidae). Ann. Entomol. Soc. Am. 93, 713-737.

OConnor, B.M., 1988. Coevolution in astigmatid mite-bee associations. In: Needham, G.R., Page, R.E., Jr., Delfinado-Baker, M., Bowman, C.E. (Eds.), African honey bees and bee mites. Ellis Horwood Ltd & John Wiley & Son, , Chichester, New York, Brisbane etc., pp. 339-346.

OConnor, B.M., 1994. Life-history modifications in astigmatid mites. In: Houck, M.A. (Ed.), Mites: ecological and evolutionary studies of life-history patterns. Chapman & Hall, New York. Chapman & Hall, New York, pp. 136-159.

OConnor, B.M., 1997. Two new mites (Acari: Acaridae) associated with long-tongued bees (Hymenoptera: Apidae) in North America. J. Kans. Entomol. Soc. 69, 15-34.

OConnor, B.M., 2001. Historical ecology of the Acaridae (Acari): phylogenetic evidence for host and habitat shifts. In: Halliday, R.B., Walter, D.E., Proctor, H.C., Norton, R.A., Colloff, M.J. (Eds.), Acarology: Proceedings of the 10th International Congress. CSIRO Publishing, Collingwood, pp. 76-82.

Turk, F.A., 1948. Insecticolous Acari from Trinidad, B.W.I. Proc. Zool. Soc. Lond. 118, 82-125.