A new genus and species of Tarsonemidae (Acari: Heterostigmata) associated with Aradus betulae (Heteroptera: Aradidae) from European Russia

of the aradid betulae (Heteroptera: Aradidae)


INTRODUCTION
The family Tarsonemidae is one of the largest groups in Heterostigmata and currently includes 42 genera and more than 600 species (Zhang et al. 2011;Lofego et al. 2016). Members of the family are phytophagous, mycophagous, parasites and parasitoids of insects, and predators preying on mite eggs (Lindquist 1986). Tarsonemid mites inhabit soils and litter, various plants, subcortical galleries of insects, etc. Many species utilize insects for phoresy (Lindquist 1986). The insect-associated Tarsonemidae of Russia are insufficiently studied. Most of them are known as associates of subcortical insects, especially bark beetles (Khaustov 1998(Khaustov , 2001Khaustov 1999, 2006;Khaustov and Magowski 2003;Khaustov et al. 2016). During the study of mites associated with insects, a new genus and species of Tarsonemidae was revealed. The aim of this article is to describe a new genus and a new species associated with the aradid bug Aradus betulae from European Russia.

MATERIALS AND METHODS
Mites were collected from under hemielytra of single specimen of an aradid bug Aradus betulae (Linnaeus, 1758) and mounted in Hoyer's medium. The terminology follows that of Lindquist (1986), except the ventral subcapitular seta is labeled su (Seeman et al. 2016). All measurements are given in micrometers (µm) for the holotype and five female paratypes (in parentheses). For leg chaetotaxy the number of solenidia is given in parentheses. DIC micrographs were taken using the Carl Zeiss Axio Imager A2 compound microscope and digital Cameras Axio-cam 506 color and Hitachi KP-HD20A. The holotypes and most paratypes of the new species are deposited in the mite collection of the Tyumen State University Museum of Zoology, Tyumen, Russia; two female paratypes of the new species are deposited in the acarological collection of the Zoological Institute of RAS, St. Petersburg, Russia.
Differential diagnosis -Females of Lobotarsonemus n. gen. resemble those of Rhynchotarsonemus Beer, 1954 from the tribe Tarsonemini in having a beaklike gnathosoma and in having legs IV much shorter than leg III. They also resemble those of Suskia Lindquist, 1986 from the tribe Steneotarsonemini in having the gnathosoma strongly prolonged, beaklike and retain seta pl" on tarsus II. Females of Lobotarsonemus differ from those of both other genera in having three large lobes on anterior part of poststernal plate, by the presence of dorsodistal projections on tarsi II and III and by absence of seta v'Fe on femorogenu IV. Females of Lobotarsonemus n. gen. also resemble those of Biscutulumnemus Lofego and Feres, 2006 from the tribe Tarsonemini in having the gnathosoma strongly prolonged, strongly reduced poststernal apodeme and retain seta pl" on tarsus II. Females of Lobotarsonemus differ from Biscutulumnemus in having three large lobes on anterior part of poststernal plate, by the presence of dorsodistal projections on tarsi II and III and by absence of seta v'Fe on femorogenu IV.
Remarks -Lobotarsonemus keys to couplet 17 of Lindquist (1986) which separates Suskia and Rhynchotarsonemus on the basis of their beak-like gnathosoma. These genera are placed in different tribes -Steneotarsonemini and Tarsonemini, respectively -showing that Lindquist (1986) thought that the beak-like gnathosoma was independently derived. Lobotarsonemus is best placed in the Steneotarsonemini because of its reduced sejugal apodeme; in the Tarsonemini this apodeme is complete. Lobotarsonemus is also closer to Suskia in its retention of a spinelike pl on tarsus II and solenidion ϕ 2 on leg I, and on femur I seta l is not enlarged, and seta v is not on a finger-like apophysis.
Male and larva unknown.
Species included -The genus Lobotarsonemus includes one species, L. betulae n. sp.
Etymology -The name of the new genus is a combination of two words, the Latin lobus meaning lobe, and Tarsonemus, the type genus of the family Tarsonemidae and refers to the presence of three unusual lobes on anterior margin of posterior sternal plate.
Etymology -The specific epithet of the new species is derived from the name of its phoretic host Aradus betulae.

DISCUSSION
Specimens of the newly described genus and species were collected under hemielytra of aradid bugs.
In our opinion, they are phoretic rather than parasitic on insect host, because junior author collected Lobotarsonemus betulae on aradid bugs only during late April and May, also we did not find eggs, males or larvae on the insect host and not observed physogastry of females.
Lobotarsonemus betulae is characterized by the presence of unusual three lobes on anterior margin of poststernal plate. This character is unknown in any tarsonemid genus. Similar lobes are known only in the genus Pseudotarsonemoides Vitzthum, 1921 (subfamily Pseudotarsonemoidinae), but in Pseudotarsonemoides there are only two lobes overlapping each over, the median lobe is absent. These lobes are very likely to be independently derived as the Pseudotarsonemoidinae is a well-defined subfamily of Tarsonemidae and Lobotarsonemus is clearly a member of the Tarsoneminae.