Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Dorsal shield entire, opisthonotal region usually hypotrichous (9–12 pairs of setae), rarely (e.g., Pseudopachyseiulus) with full J, Z and S complements
• Tibia I and genu I each with 2 anterolateral setae; tibia I with 5 dorsal setae (rarely 6 = Zygoseius, Pachyseiulus, Pseudopachyseiulus).
• Arthrodial process weakly formed, rarely brush-like
• Legs I with ambulacra
• Male femur II with spur; peritreme linear.
• Female ventral shields are variously formed, but in the genera above the metasternal setae (st4) are usually fused to the sternal shield (free in soft cuticle in Pseudopachyseiulus), such that it bears 4 pairs of setae, the genital shield is expanded and bears 2 pairs of setae, and the peritrematal shields extend posterior to coxae IV

Simplified key to common genera of Pachylaelapidae

1. Females (and usually males) with spur-like distal setae on tarsus II.............................. 3
   - Spur-like setae on tarsus II absent.............................. 2

2. Female with subcordate ventrianal shield with 13 setae (ZV1–2, JV1–3 + circumanals); genital shield truncate posteriorly and bearing 1 pair of setae; sternal shield with 3 pairs of setae and convex posterior margin; metasternal setae on metasternal-endopodal shield; free-living or on dung beetles.............................. Zygoseius
   - Female with anal shield (rarely capturing 1–2 ventral setae); opisthogenital shield spreading laterally, with 2 pairs of setae and recurved posterior margin; associated with ants.............................. Sphaerolaelaps

3. Female sternal shield bearing 4 pairs of setae, opisthogenital shield with 2 or more pairs of setae, and anal shield with 3 circumanal setae.............................. 4
   - Female sternal shield bearing 3 pairs of setae (st4 on small metasternal shield or in soft cuticle), genital shield with 1 pair of seta, and ventrianal shield with 7–10 setae.............................. Pachyseius

4. Tibia I with 5 dorsal setae; palp apotele 3-tined.............................. 5
   - Tibia I with 6 dorsal setae; palp apotele 2-tined.............................. 6

5. Genu I with 5 dorsal setae.............................. Onchodellus
   - Genu I with 6 dorsal setae.............................. Pachylaelaps

6. Seta st4 on small metasternal plate; dorsal shield with 37 pairs of setae.............................. Pachyseiulus
   - Seta st4 on in soft cuticle; dorsal shield with 35 pairs of setae.............................. Pseudopachyseiulus

Diagnosis

Yellow to brown dermanyssine mesostigmatans with holodorsal shields. Peritremes generally well developed, peritrematal-exopodal shields often produced posteriorly. Sternal shield often fused to posterior endopodal elements and bearing 3 or 4 pairs of setae (st1–3, +/- 4) and 2–3 pairs of lyrifissures; metasternal seta st4 in soft cuticle (e.g., Pseudopachyseiulus), on a metasternal shield, (e.g., Pachyseius), on sternal shield (e.g., Pachylaelaps, Pachyseiulus), or on endopodal-metasternal shield (e.g., Zygoseius; genital shield usually trapezoidal, subrectangular to oval-tongue-shaped; recurved to truncate posteriorly; and bearing 1–2 (rarely more) pair of setae; ventrianal shield broad with several pairs of ventral setae to small, triangular and bearing only 3 circumanal setae. Tarsus I with claws; trochanter I with 6 setae; tibia and genu I each with 5–6/3 dorsal/ ventral setae; genu IV with 8–9 setae, 4–5/1 dorsal/ ventral; leg II usually enlarged and tarsus II sometimes with spine-like distal setae. Chelicerae chelate-dentate; movable digit without excrescences, arthrodial corona not produced in a brush. Palp genu with 6 setae, palp apotele 2 or 3-tined; corniculi horn-like, often phytoseioid. Tritosternum biflagellate with columnar base. Tectum U-shaped with laterally denticulate tines. Female sperm induction pores near bases of coxae III–IV. Males with genital opening at base of tritosternum in sternogenital shield; spermatodactyl usually well developed.

Similar taxa

Many pachylaelapids have sternal shields with 4 pairs of setae, as in the Rhodacaroidea and in some Parholaspididae, but these mites usually have ventrianal rather than anal shields. Species of Zygoseius are superficially similar to ascid mites in the genus Lasioseius, but the latter never have st4 on metasternal-endopodal plates, a characteristic of the former. Some members of the Leptolaelapidae Karg may belong to the Pachylaelapidae.

References

• Gomaa et al. 1989Gomaa et al. 1989:
  Gomaa EA, Abou Awad BA, Nasr AK, Abou Elela MM. 1989. Life-history studies and feeding behavior of the predatory mite, Pachylaelaps aegyptiacus, with description of immature stages (Acari: Pachylaelapidae). Insect Science and its Application 10 (5): 691–698.
• Gu and Bai 1995Gu and Bai 1995:
  Gu Y-M, Bai X-I. 1995. Two new records of Pachylaelaps from China (Acari: Pachylaelapidae). Acta Zootaxonomica Sinica 20: 450.
• Halliday 1997bHalliday 1997b:
  Halliday RB. 1997b. Revision of the genus Zygoseius Berlese (Acarina: Pachylaelapidae). Acarologia 38: 3–20.
• Moraza 1993Moraza 1993:
  Moraza ML. 1993. Two new species of Pachyseius Berlese, 1910 from Spain (Acari, Mesostigmata: Pachylaelapidae). Acarologia 34: 89–94.
• Moraza and Johnston 1990Moraza and Johnston 1990:
  Moraza ML, Johnston DE. 1990. Pachyseiulus hispanicus n. gen., n. sp., from Navarre (northern Spain) (Acari: Mesostigmata: Pachylaelapidae). International Journal of Acarology 16: 213–218.
• Moraza and Johnston 1993Moraza and Johnston 1993:
  Moraza ML, Johnston DE. 1993. Pseudopachyseiulus ignacii n. gen., n. sp., from Navarra (northern Spain) (Acari: Mesostigmata: Pachylaelapidae). Redia 76: 263–271.
• Womersley 1942Womersley 1942:
  Womersley H. 1942. Additions to the Acarina-Parasitoidea of Australia. Part I. Transactions of the Royal Society of South Australia 66: 142–171.
• Yin et al. 1986Yin et al. 1986:
  Yin S-G, Luc J, Lian W-H. 1986. A new species and a new record of the genus Pachyseius from China (Acarina: Pachylaelapidae). Acta Zootaxonomica Sinica 11 (2): 191–193.