Schizotetranychus-like spider mites (Acari, Prostigmata, Tetranychidae) - revisited, new combinations and a key to groups of Schizotetranychus based on females

An overview of Schizotetranychus-like acarina is presented, with a key to the major groups of Schizotetranychus of the world, based on females. A probable remnant of the dorsal parts of the podal segments III and IV in Stigmaeopsis species is discussed. New combinations are proposed.


INTRODUCTION
The genus Schizotetranychus is one with the largest number of species, 115 (Migeon andDorkeld, 2006-2011) of the family Tetranychidae. The identification of species in this genus has conventionally been based primarily on characters of the male aedeagus. Similarly as has been proposed for the species in the genus Tetranychus by Flechtmann and Knihinicki (2002) for cases where male specimens are not available or traditional characters such as the aedeagus shape are not reliable, an arbitrary key, based only on females, to the major groups of Schizotetranychus could help complement existing keys.
HISTORICAL REVIEW OF THE Schizotetranychus-LIKE GENERA Trägårdh (1915), based on the shapes of the ambulacra of Tetranychidae with 7 setiform structures on the palpal tarsus ("2 sensory cones, 2 straight pinshaped hairs, 3 ordinary hairs") and the presence of 10 pairs of dorsohysterosomal setae, until then placed in Paratetranychus Zacher and Tetranychus Dufour, divided this group creating two new genera, Neotetranychus and Schizotetranychus. For their recognition he proposed the following key: Key to genera, (from Trägårdh, 1915)  -Claw divided into 4-6 prongs . Tetranychus Dufour Ehara (1978) described a tetranychid genus Yezonychus, type Y. sapporensis Ehara, with the above characters of Schizotetranychus but which has no f2 (outer sacral) setae, a pair of dorsohysterosomal setae present in Schizotetranychus. Its empodium is clawlike, split into two equal halves over about half of its length. This genus remains monotypic. Ma and Gao (1985) described the genus Yunonychus, type Y. daliensis Ma and Gao, also with the above characters of Schizotetranychus but without setae c2 (first pair of hysterosomal sub-lateral setae). This genus remains monotypic. Zhang and Martin (2001) erected the genus Tribolonychus, type T. collyerae Zhang and Martin, lacking setae f2 (as in Yezonychus), but with a clawlike trifid empodium, that is, split into three prongs, two lateral, smaller, and one dorsomedian prong. This genus also remains monotypic. Beard and Walter (2010) described Neonidulus, the fourth genus split off from Schizotetranychus, where setae f2 are missing and with a clawlike empodium entirely (deeply) split into two clawlike structures, each with three prongs; the ventral prong on each pair much thicker than the two dorsal prongs. Type species Schizotetranychus cornus Pritchard and Baker, 1955. The authors also described one new species in this genus, N. tereotus, and transferred two species, formerly placed in Yezonychus, to this genus: N. brevipilus (Zhang and Martin, 2001) and N. falsicornus (Zhang and Martin, 2001).
The remaining species, with the characters mentioned in the first paragraph and presenting nine pairs of dorsal hysterosomal setae (c 1-2-3, d 1-2, e 1-2 and f 1-2) were left in the genus Schizotetranychus Trägårdh, 1915, type species Tetranychus schizopus Zacher, 1913. McGregor (1950 synonymized Stigmaeopsis Banks, 1917(type species S. celarius Banks, 1917 under Schizotetranychus. Saito et al. (2004) reinstated the genus Stigmaeopsis Banks based on the presence of only six setiform structures on the palp tarsus of females and males (2 simple setae, 3 eupathidia and one solenidion), while there are seven of these structures (three simple setae + ...) in Schizotetranychus. The seven species now recognized as Stigmaeopsis, S. celarius Banks, S. longus (Saito, 1990), S. miscanthi (Saito, 1990), S. nanjingensis (Ma and Yuan, 1980), S. tenuinidus (Zhang and Zhang, 2000), S. saharai Saito andMori, 2004 andS. takahashi Saito andMori, 2004 are also characterized by the position of the dorsocentral hysterosomal setae: the bases of the pairs of setae e1, d1 and c1 are progressively wider apart than the bases of f1 setae, that is, hypothetical lines connecting their bases form a V shaped pattern (these lines are parallell in the other Tetranychini, including Schizotetranychus), as pointed out by Saito et al. (2004). Another striking feature exhibited by the Stigmaeopsis species is the dorsal integumental trapezoidal area between the pairs of setae c1, d1 and e1. Anteriorly this area is well set off from the propodosoma dorsum by the sejugal furrow; laterally there seems to be no well pronounced furrows or deep markings and posteriorly, at least in S. celarius, S. saharai, S. takahashii there seems to occur another, although short, transverse furrow. The exact nature of these lateral and posterior limits should be examined in specimens not flattened by the weight of the coverslip. This trapezoidal area is clearly longitudinally striated, the striae restricted to this area, while the lateral adjacent areas, bearing the dorsohysterosomal setae, although mainly longitudinally striated, their striae bend anteriorly outwards and posteriorly around the central trapezoidal area. Could this trapezoidal area represent a remnant of the dorsal part of the podal segments of legs III and IV?
Due to insufficient data provided in their descriptions the following species could not be affiliated to any of the above groups: -S. setariae Meyer, 1987 -only known from the male.
-S. emeiensis Wang, 1983 female has nine tactile and two sensory setae on tibia of leg I ; otherwise it would fit into group 17.
-S. tuberculatus (Ugarov and Nikolski, 1937)is the only species where the dorsal setae are set on tubercles.
-S. jachontovi Reck, 1953 belongs to one of the groups in between 14 and 17; no information on the number of tibial setae is given in its description.