Pachyseius Berlese, 1910

MAŠÁN, PETER & HALLIDAY, BRUCE, 2014, Review of the mite family Pachylaelapidae (Acari: Mesostigmata), Zootaxa 3776 (1), pp. 1-66 : 41

Genus Pachyseius Berlese, 1910

Pachyseius Berlese, 1910a: 255 .

Type species Pachyseius humeralis Berlese, 1910 , by original designation.

The genus Pachyseius was proposed by Berlese (1910a), but has sometimes been considered as a synonym of Neoparasitus Oudemans, 1901 in the family Neoparasitidae Oudemans, 1939 , for example by Vitzthum (1942) and Baker & Wharton (1952). Evans (1957a) placed Pachyseius as a separate genus in a very broad and heterogeneous family Neoparasitidae . Later Evans & Till (1979) placed this genus in the family Pachylaelapidae , but Karg (1971, 1993) placed Pachyseius in the family Macrochelidae rather than the Pachylaelapidae . Karg (1971) proposed a separate tribe Pachyseiini Karg, 1971 for the genus Pachyseius , primarily because of the simple form of the epistome, short dorsal setae, straight peritremes, and fused ventral and anal shields. Although most other authors have placed Pachyseius in the family Pachylaelapidae , the systematic position of the genus in the family seems to be fragile and provisional. Mašán (2007a) placed it in the subfamily Pachyseiinae , and that usage is followed here. The relationship of Pachyseius to the other genera of Pachylaelapid is unclear. On the basis of the recently described species ( Mašán & Mihál, 2007), it appears that the general evolutionary trend in Pachyseius is towards increased sclerotisation, including fusion of some ventral shield components to form a contiguous exopodalperitrematal complex, a sternal-metasternal complex, and abnormally large metapodal platelets widely abutting the parapodal platelets and ventri-anal shield.

Pachyseius is distributed exclusively throughout the Palaearctic region, except that Pachyseius humeralis may have been introduced into Australia by human activities ( Halliday, 2001), and unidentified species have been collected in northern Australia ( Lindquist et al., 2009) and Canada (Broadbent & Tomlin, 1979). It currently comprises 17 known species from Europe, Russia, China and Japan.