Tetranychus, Dufour, 1832

SEEMAN, OWEN D. & BEARD, JENNIFER J., 2011, Identification of exotic pest and Australian native and naturalised species of Tetranychus (Acari: Tetranychidae), Zootaxa 2961 (1), pp. 1-72 : 12

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https://doi.org/ 10.11646/zootaxa.2961.1.1

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Distinguishing Tetranychus from other Tetranychidae

The family Tetranychidae is split into two subfamilies, the Bryobiinae and Tetranychinae , with Tetranychus belonging to the latter subfamily. The subfamilies are distinguished by the form of the empodia in the female mite: tenent hairs are present on the empodium in Bryobiinae ( Fig. 3A, B) but absent on the empodium in Tetranychinae ( Fig. 3C–H). In the Tetranychinae , the empodium may be absent ( Fig. 3C), claw-like ( Fig. 3E–F), comprising fine hairs only (empodial or proximoventral hairs) ( Fig. 3G), a claw with basal fine hairs (empodial or proximoventral hairs) ( Fig. 3H), or it can have a dorsal spur ( Fig. 3D)—but it never has tenent hairs. Tetranychus tends to have an empodium consisting of proximoventral hairs with or without a dorsal spur ( Fig. 3G), except for the male empodium I (and sometimes II) where it is claw-like ( Fig. 3D, F). The dorsal spur on the empodium of Tetranychus is usually small, but ranges from absent to obvious in different species, and is a useful diagnostic character.

After determining the structure of the empodium, the next step is to look for dorsal seta h1. Setal rows c, d and e form clearly transverse rows, but those of f and h are curved ( Fig. 5). Row h is curved so much that setae h3, and sometimes h2, are placed on the ventral side of the mite ( Fig. 5b). When determining if h1 is present, start at row c and count through the rows until row h is reached. If setae h1 are present, they will be inserted centrally in the next setal row behind f1. Setae h1 when present tend to be the same morphology as the other dorsal setae, whereas setae h2 and h3 are shorter and thinner than h1, and are inserted more laterally (and/or ventrally) than h1 ( Fig. 5a). Setae h2 and h3 are often lateral of the anus ( Fig. 6). Only two genera, Tetranychus and Amphitetranychus Oudemans, 1931 , have the combination of empodia comprising just fine hairs ( Fig. 3G) and h1 absent. These two genera can be distinguished by their peritremes: in Tetranychus they are hook-like (Fig. 8), but in Amphitetranychus they are anastomosing (branching) and protrude from the anterior margin of the prodorsum. Amphitetranychus is absent in Australia and contains the economically-important species A. viennensis ( Zacher, 1920) .’