Thinoseius Halbert, 1920

Halliday, R. B., 2010, Revision of the Australian Eviphididae (Acari: Mesostigmata) 2596, Zootaxa 2596 (1), pp. 1-60 : 33-34

Genus Thinoseius Halbert

Thinoseius Halbert, 1920: 111 .

Type species Thinoseius berlesei Halbert, 1920: 111 , by original designation (as berlesii).

Ligialaelaps Radford, 1942: 298 . Synonymy by Bregetova (1977).

Type species Eulaelaps ewingi Pearse, 1930: 6 , by original designation.

Gammaridacarus Canaris, 1962: 467 . Synonymy by Evans (1963b).

Type species Gammaridacarus brevisternalis Canaris, 1962: 467 , by monotypy.

Diagnosis of genus. Eviphididae in which the sternal shield is reduced or absent, or with a sclerotised remnant of the shield bearing one or two pairs of sternal setae. The epistome has five or more long anterior projections, most of which have multidentate tips. Palp genu with five setae; femur II with one anterolateral seta; femur III with two ventral setae.

Notes on the genus. Thinoseius is a genus of 13 species from Europe ( Evans & Browning 1953; Bregetova 1977; Błaszak et al. 2004), the Middle East ( Hirschmann 1966), Japan ( Takaku 2000), New Zealand ( Evans 1969), subantarctic islands ( Hunter 1970) and USA ( Hennessey & Farrier 1988). The only species known from the Southern Hemisphere are T. ramsayi Evans 1969 from New Zealand ( Evans 1969; Luxton 1990), and T. hirschmanni Hunter 1970 and T. katherinae Hunter 1970 from South Georgia. All species are found in seaweed in the intertidal zone on beaches and rocky shores. They are often phoretic on crustaceans, either amphipods (e. g. T. brevisternalis ( Canaris 1962) ( Rigby 1996)) , or isopods (e. g. T. setifer Takaku 2000 ), which they use for dispersal. Rigby (1996) showed that T. brevisternalis feeds on rhabditid nematodes, which are also phoretic on their amphipod host. Species of Thinoseius are also sometimes phoretic on kelp flies of the families Coelopidae ( Egglishaw 1960; Dobson 1976) and Anthomyidae ( Roth & Brown 1976). Most of the known species were included in the key of Evans (1969). The identification of species of Thinoseius is complicated by the strong sexual dimorphism in most species, and by the fact that some species are incompletely known. Thinoseius schusteri Hirschmann 1966 and T. katherinae are known only from the deutonymph, and the descriptions of T. ewingi ( Pearse 1930) and T. orchestoideae ( Hall 1912) are not detailed enough to allow their recognition. Thinoseius sawadai Takaku 2000 and T. setifer were both described from their males and deutonymphs, and their females are unknown.

The present study includes collections of Thinoseius from four coastal areas in southeastern Australia ( Fig. 36 ). The females from these areas can be recognised as belonging to five distinct species. Collections were taken from suburban beaches of the city of Adelaide, South Australia (Largs Bay, one species of Thinoseius ), southeastern South Australia (Robe, Kingston, Cape Jaffa, Nora Creina, four species), Mallacoota, in eastern Victoria (Betka Beach, Bastion Point, two species), and the south coast of New South Wales (Batemans Bay area, two species). These collections all included adult females, adult males, and nymphs. The adult males can be sorted into five species, which presumably correspond to the five species of females. However, the presence of more than one species at most collecting sites, combined with the strong sexual dimorphism in Thinoseius , makes it difficult to confidently associate the males and immatures with the females of most of these species. Only one species of Thinoseius was present in the collections from Adelaide, so I here describe the female, male, deutonymph and protonymph of T. jarretti sp. nov. from that area. The females of the other four species are here described as T. helenae sp. nov., T. papillatus sp. nov., T. peltatus sp. nov. and T. variabilis sp. nov.. Thinoseius helenae was abundant in the southeast of South Australia and occurred nowhere else. A type of male with spatulate setae on the dorsal shield was also abundant in this area and occurred nowhere else, so this male is described as that of T. helenae . The other three types of males cannot be identified to species (see Discussion).

The seaweed samples I collected for this study contained multiple species of insects, especially Coleoptera and Diptera , as well as spiders, crustaceans, and other fauna. I examined many hundreds of specimens of these animals, to look for attached mites. The only specimens that had visible mites attached to their bodies were flies of the family Sphaeroceridae , ( Fig. 52 ). I observed 72 such flies carrying deutonymphs of Thinoseius ; 70 of these flies were Thoracochaeta brachystoma (Stenhammar) and two were Thoracochaeta neofucicola Marshall & Roháček. Most of the flies that were carrying mites (53) carried only one mite, but some carried two (11) or three (6), and two flies carried four mites each. The mites attached themselves to the fly using their chelicerae to grip a fold of soft skin in the intersegmental membrane at the anterior end of the fly's abdomen.

These phoretic deutonymphs have not been identified to species, because they cannot be correlated with their adult females with any certainty. Phoretic mites were observed on flies in the southeast of South Australia, and in New South Wales, and more than one species of Thinoseius occurs in both of these areas. In both these areas, the phoretic deutonymphs were very variable in the morphology of their dorsal shield setae. Setae in the J series in different specimens varied from short and fine to very long, heavy, and sword-like, suggesting that more than one species of Thinoseius was practising phoresy in each area. It is also impossible to identify the species of Thinoseius reported by McAlpine (1991), from laboratory cultures of the kelp fly Rhis whitleyi , since the specimens from that source are all deutonymphs.

Figures

FIGURE 36. Distribution records of Scarabaspis sternalis. 1–21 = populations in which dorsal shield ornamentation was studied. Details in Table 1. Other localities as mentioned in text.

FIGURE 52. Deutonymphs of Thinosieus sp. phoretic on a fly, Thoracochaeta brachystoma, McKenzies Beach, New South Wales. (photo by Natalie Barnett). Scale bar = 500 µm.