Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Melicharinae with a free ventral plate in the adult female

Similar taxa

Proctogastrolaelaps appear to be intermediate between Proctolaelaps (anal shield, no ventral shield) and Paraproctolaelaps (anal and ventral shields fused into a ventrianal shield). Free ventral plates are very rare in the Monogynaspida, but do occur in the unusual phytoseiid genus Iphiseius (with the strongly reduced dorsal shield chaetome characteristic of Phytoseiidae and a phytoseiid-type of sperm access system) and in some Veigaiidae (palp apotele 3–4 tines and with scale-like process).

Key to the genera of Melicharinae

1. Idiosoma narrow, dorsal shield greater than twice as long as wide; leg setation strongly neotenous, genua I–II–III–IV with 12–7–6–7 setae, tibiae with 11–7–6–6 setae; female lacking metasternal plates and with ventri-anal shield bearing 1–3 pairs of ventral setae in addition to circumanal setae.............................. Mycolaelaps
   - Idiosoma broader, legs not strongly neotenous, metasternal plates present or absent, only anal shield or separate anal and ventral shields.............................. 2

2. Female with separate ventral shield bearing 4 pairs of setae between genital and anal shields; posterior connection of peritrematal shield to exopodal plate beside coxa IV broad (subequal to width of stigma); corniculi slender, acute; rows of deutosternal denticles narrow, in deep trough; epistome convex, smooth; movable chela of female unidentate.............................. Proctogastrolaelaps
   - Ventral area not sclerotized, only small anal shield with 3 circumanal setae present.............................. 3

3. Fixed chela of female and nymphs with pointed or rounded flange-like projection distally; leg IV with 1 or 2 erect macrosetae on telotarsus (pd2, +/- ad2); 3rd pair of sternal pores absent.............................. Mucroseius
   - Fixed chela without distal flange-like projection; leg IV usually without macrosetae; 3rd pair of sternal pores usually present.............................. 4

4. Dorsal shield of adults with pair of deep midlateral incisions, lacking setae z3 on podonotal region; movable chela with 0 or 1 tooth; female without metasternal plates.............................. 6
   - Dorsal shield of adults entire, usually with setae z3 on podonotal region; movable chela with 3 teeth; with or without metasternal plates.............................. 5

5. Adults with 7–13 pairs of marginal (r–R) setae on soft lateral cuticle (rarely fewer if some r–R setae lacking); female with 14–15 pairs of setae on opisthonotal region of dorsal shield and lacking metasternal plates (except in Orolaelaps).............................. Melichares
   - Adults with 1–4 pairs of posterior marginal (R) setae on soft ventro-lateral cuticle, all others on edge of dorsal shield; female with 18–22 pairs of setae on opisthonotal region of dorsal shield; female usually with metasternal plates.............................. Proctolaelaps

6. Movable chela unidentate; female with 1st pair of sternal setae on soft cuticle in front of sternal shield; male with separate ventral & anal shields; male leg II with tarsal seta pv1 unmodified.............................. Xanthippe
   - Movable chela edentate; female with first pair of sternal setae on sternal shield; male usually with consolidated ventrianal shield; male leg II with apical tarsal seta pv–1 slightly to conspicuously thickened.............................. 7

7. Tibiae III and IV with 9 and 10 setae respectively (pl2 present); dorsal shield with setae s6; female with hyaline anterior margin of epigynial shield rounded, and with genital setae on lateral edges of this shield; male tarsus II with seta pv–1 knob- or spine-like, and tarsus III with 1–3 setae (always av2) knob-like; male spermatodactyl directed anteriorly.............................. Tropicoseius
   - Tibiae III and IV with 8 and 9 setae respectively (pl2 absent); dorsal shield lacking setae s6; female with hyaline anterior margin of epigynial shield usually truncated or emarginated, and with genital setae on soft cuticle flanking this shield; male tarsus II with seta pv1 but slightly thickened, and tarsus III without modified setae; male spermatodactyl directed posteroventrally.............................. Rhinoseius

References

• Evans and Till 1979Evans and Till 1979:
  Evans EO, Till WM. 1979. Mesostigmatic mites of Britain and Ireland (Chelicerata: Acari-Parasitiformes): An introduction to their external morphology and classification. Transactions of the Zoological Society of London 35 (2): 145–270.
• Halliday et al. 1998Halliday et al. 1998:
  Halliday RB, Walter DE, Lindquist EE. 1998. Revision of the Australian Ascidae (Acarina: Mesostigmata). Invertebrate Taxonomy 12: 1–54.
• Karg 1993Karg 1993:
  Karg W. 1993. Acari (Acarina), Milben Parasitiformes (Anactinochaeta) Cohors Gamasina Leach, Raubmilben. Die Tierwelt Deutschlands 59: 1–523.
• Krantz 1986Krantz 1986:
  Krantz GW. 1986. A manual of acarology [2nd ed., emended 1986]. Oregon State University Book Stores, Corvallis.
• Krantz and Ainscough 1990Krantz and Ainscough 1990:
  Krantz GW, Ainscough B. 1990. Mesostigmata. pp. 583–665. In: Dindal DL, ed. Soil biology guide. John Wiley & Sons, Brisbane.
• Lindquist and Evans 1965Lindquist and Evans 1965:
  Lindquist EE, Evans GO. 1965. Taxonomic concepts in the Ascidae, with a modified setal nomenclature for the idiosoma of the Gamasina (Acarina: Mesostigmata). Memoirs of the Entomological Society of Canada 47: 1–64
• McGraw and Farrier 1969McGraw and Farrier 1969:
  McGraw JR, Farrier MH. 1969. Of the superfamily Parasitoidea (Acarina: Mesostigmata) associated with Dendroctonus and Ips (Coleoptera: Scolytidae). North Carolina Agricultural Experiment Station Technical Bulletin No. 192, 162 pp.