Belongs within: Microtrombidiidae.
Microtrombidium is a cosmopolitan genus of predatory mites, primarily recognised from adults with the larva of M. nitidum only described in 1994. Though numerous species have been assigned to the genus historically, the position of many requires further assessment (Southcott 1994). The European effective type species M. pusillum is characterised by as an adult by a uniform pelage of soft, fine hairs and palptibiae without a spine on the outer side. Microtrombidium aquarium has a single weak spine on the outer side of the palptibia and a long hair distally on the palptarsus (Schweizer & Bader 1963).
Characters (from Southcott 1994): Adult/deutonymph with idiosoma with more or less uniform pelage of strongly setulose setae, unexpanded, unchambered, pointed or blunted; palpal tibia with odontus and paradont, and one or more dorsomedial ctenidia; legs I and IV longer than II and III, and not greatly longer than idiosomal length. Larva with anterior dorsal scutum with six scutalae and two sensillary setae; posterior dorsal scutum with two scutalae; both scuta porose, without striations or special markings; anterior dorsal scutum with posterolateral border emarginate, accomodating well-developed eye shields; anterior eye significantly larger than posterior; at least some of dorsal idiosomal setae posterior to posterior dorsal scutum with well-developed basal plates; two ventral intercoxalae between coxae III; coxalae 2, 1, 1, formula bN, b, N; two solenotibialae at about middle of tibia I; Tarsal claws 2, 2, 3 (deformed); tarsus III abbreviated, not truncate; hypostomala pointed, not digitate.
<==Microtrombidium Haller 1882H98 [=Microthrombidium Oudemans 1912S94] |--M. pusillum (Hermann 1804)S94 (see below for synonymy) | |--M. p. pusillumSB63 | `--M. p. botschi Schweizer & Bader 1963SB63 |--M. affine Hirst 1928H98 |--M. akamushiW34 |--M. aquarium Schweizer 1951SB63 |--M. arborealis Boshell & Kerr 1942M46 |--M. aucklandicum Luxton 1989L90 |--M. barringunense Hirst 1928H98 |--M. basiliense Schweizer & Bader 1963SB63 |--M. berlesei Schweizer 1922S22 |--‘Trombidium’ bipectinatum [=Enemothrombium bipectinatum]O28 |--M. bispinum Schweizer & Bader 1963SB63 |--M. cinctipalpumL89 |--M. cookiDPD16 |--M. cruentatum Berlese 1910 [=M. (Enemothrombium) cruentatum]G96 |--M. danbyiWL09 |--M. duarteiM46 |--M. eutrichum [=M. (Enemothrombium) eutrichum]G96 |--M. furcipilis (Canestrini 1898) [=Ottonia furcipilis, Microthrombidium furcipilis, Microtrombidium furcipile]H98 |--M. geographicumS22 |--M. goodenoughenseS94 |--M. hirsutum Womersley 1945H98 |--M. jabanicum Berlese 1910 [=M. pusillum var. jabanicum]S76 |--M. karriense Womersley 1934 [=M. karriensis, Elahistothrombium karriense]H98 |--M. littorale Michener 1946H60 |--M. maculatum Womersley 1942H98 |--M. malindiensis Luxton 1989L89 |--M. medium Schweizer & Bader 1963SB63 |--M. myloriense Womersley 1937H98 |--M. newmani Womersley 1934H98 [=M. (Enemothrombium) newmaniW34] |--M. nitidum Southcott 1994H98 |--M. otagoensis Luxton 1989L90 |--M. parvum Oudemans 1913SB63 |--M. quadrispinum Berlese 1910SB63 |--M. raeticum Schweizer & Bader 1963SB63 |--M. soperiM46 |--M. stimulansM46 |--M. subferociforme Schweizer & Bader 1963SB63 |--M. tasmanicum Womersley 1937H98 |--M. tenuipalpe Schweizer & Bader 1963SB63 |--M. triangulum Howard 1919S94 |--M. tredecimmaculatumM46 |--M. welleslyiWL09 |--M. wellingtonense Womersley 1945H98 `--M. zelandicum Womersley 1936L89
Microtrombidium pusillum (Hermann 1804)S94 [=Trombidium pusillumS94, Ottonia pusillaTU33; incl. M. pusillum var. balzaniS22, M. pusillum var. columbianumS22, M. pusillum var. minor Schweizer 1922S94, T. purpureum Haller 1882 non Trombidium purpureum Koch 1837SB63, *M. purpureumS94]
*Type species of generic name indicated
References
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[G96] Gabrys, G. 1996. Does Enemothrombium Berlese, 1910 (Microtrombidiidae) have the right to exist? In: Mitchell, R., D. J. Horn, G. R. Needham & W. C. Welbourn (eds) Acarology IX vol. 1. Proceedings pp. 363–365. Ohio Biological Survey: Columbus (Ohio).
[H98] Halliday, R. B. 1998. Mites of Australia: A checklist and bibliography. CSIRO Publishing: Collingwood.
[H60] Hammen, L. van der. 1960. Fortuynia marina nov. gen., nov. spec., an oribatid mite from the intertidal zone in Netherlands New Guinea. Zoologische Mededelingen 37 (1): 1–9.
[L89] Luxton, M. 1989. New taxa of intertidal mites (Acari). Journal of Natural History 23: 407–428.
[L90] Luxton, M. 1990. The marine littoral mites of the New Zealand region. Journal of the Royal Society of New Zealand 20 (4): 367–418.
[M46] Michener, C. D. 1946. The taxonomy and bionomics of some Panamanian trombidiid mites. Annals of the Entomological Society of America 39: 349–380.
[O28] Oudemans, A. C. 1928. Fauna Buruana. Acari. Treubia 7 (Suppl. 2): 37–100.
[S22] Schweizer, J. 1922. Beitrag zur Kenntnis der terrestrischen Milbenfauna der Schweiz. Verhandl. Naturf. Ges. Basel 33: 23–112, 4 pls.
[SB63] Schweizer, J., & C. Bader. 1963. Die Landmilben der Schweiz (Mittelland, Jura und Alpen): Trombidiformes Reuter, mit 217 Arten und Unterarten und 193 Originalzeichnungen. Denkschriften der Schweizerischen Naturforschenden Gesellschaft [Mémoires de la Société Helvétique des Sciences Naturelles] 84 (2): i–vi, 209–378.
[S76] Shiba, M. 1976. Taxonomic investigation on free-living Prostigmata from the Malay Peninsula. Nature and Life in Southeast Asia 7: 83–229.
[S94] Southcott, R. V. 1994. Revision of the larvae of the Microtrombidiinae (Acarina, Microtrombidiidae), with notes on life histories. Zoologica 48 (2): 1–155.
[WL09] Walter, D. E., E. E. Lindquist, I. M. Smith, D. R. Cook & G. W. Krantz. 2009. Order Trombidiformes. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3rd ed. pp. 233–420. Texas Tech University Press.
[W34] Womersley, H. 1934. A revision of the trombid and erythraeid mites of Australia with descriptions of new genera and species. Records of the South Australian Museum 5 (2): 179–254.