A new species of Tarsonemus (Acari: Tarsonemidae) associated with the bark beetle, Polygraphus proximus (Coleoptera: Curculionidae: Scolytinae) from the Far East of Russia

Larvae, males and females of a new species from the minimax species-group, Tarsonemus striatus n. sp. (Acari: Tarsonemidae) are described from the galleries of, and phoretic on, the bark beetle Polygraphus proximus Blandford, 1894 (Coleoptera: Curculionidae: Scolytinae) in the Far East of Russia.


INTRODUCTION
Four-eyed fir bark beetle, Polygraphus proximus Blandford, 1894, is an invasive species and has become the major cause of death of fir trees in the Siberian and European parts of Russia (Kerchev 2014;Kononov et al. 2016). Originally inhabiting the Far East of Eurasia and nearby islands, including the Russian Far East, P. proximus has rapidly expanded its distribution westward (Kerchev 2014). Despite high economic importance of the four-eyed fir bark beetle, nothing is known about mites associated with it. During the study of mites associated with P. proximus, a new species, Tarsonemus striatus n. sp. (Acari: Tarsonemidae) from the minimax species-group, was revealed in native populations of the four-eyed fir bark beetle in the Far East of Russia.
The genus Tarsonemus Canestrini and Fanzago, 1876 is the largest in the family Tarsonemidae and includes more than 270 species (Lin and Zhang 2002;Magowski 2002Magowski , 2010Lofego et al. 2005). Some Tarsonemus mites are known as a vector for the dispersal of fungal spores, carrying them in sporothecae located under the lateral parts of tergite C in females. Potentially they can carrying fungal spores on cerotegument on prodorsum and tergites C and D as was recently discovered by Rezende et al. (2015) for the genera Daidalotarsonemus De Leon and Excelsotarsonemus Ochoa and Naskręcki. The best studied case is the mutualistic association of Tarsonemus krantzi Smiley andMoser, 1974 andT. ips Lindquist, 1969 with Ophiostoma minus (Hedgcock) Syd. & P. Syd associated with southern pine beetle (Dendroctonus frontalis Zimmermann, 1968) in North America (Lombardero et al. 2003). Lindquist (1986) divided the genus Tarsonemus into three subgenera: Tarsonemus s. str., Chaetotarson-emus Beer and Nucifora, 1965and Floridotarsonemus Attiah, 1970. Magowski (2010 created the subgenus Schaarschmidtia Magowski, 2010, which includes species previously placed in the pyrrhidi speciesgroup of the subgenus Tarsonemus (Magowski and Moser 2003).
The minimax species-group currently includes nine species: T. minimax Vitzthum, 1926, T. crassus (Schaarschmidt, 1959, T. triarcus Lindquist, 1969, T. subcorticalis Lindquist, 1969, T. endophloeus Lindquist, 1969, T. krantzi Smiley and Moser, 1974, T. suskii Smiley and Moser, 1974, T. terebrans Magowski and Moser, 2003, and T. typographi Magowski and Moser, 2003(Magowski and Moser 2003. Magowski and Moser (2003) reviewed the minimax species-group and provided a key to its species. Most species of minimax species-group are associated with various bark beetles and distributed in Holarctic (Lindquist 1969;Smiley and Moser 1974;Magowski and Moser 2003). Detailed distribution and host range is discussed in Magowski and Moser (2003). The morphological distinctions between minimax species-group and other groups within subgenus Tarsonemus are not clearly defined because no differential diagnosis was provided in Magowski and Moser (2003). Magowski and Moser (2003) suggested that members of the minimax species-group are similar to the gladifer and floricolus species-groups, but the reference of two latter groups is an unpublished work of Magowski. Despite such vague diagnosis of minimax speciesgroup, Tarsonemus striatus n. sp. undoubtedly belongs to this group because of the morphological similarity to T. triarcus, the member of this group, and similar ecology.
The aim of this article is to describe all developmental stages of Tarsonemus striatus n. sp. associated with the bark beetle Polygraphus proximus.

Pieces of bark of Manchurian fir (Abies nephrolepis)
containing adult four-eyed fir bark beetle (Polygraphus proximus) and its galleries were placed in plastic boxes and transported to the laboratory. In the laboratory pieces of bark and living beetles were inspected for mites using a Discovery V8 (Carl Zeiss, Germany) stereomicroscope. Most of the collected mites were mounted in Hoyer's medium. Some living beetles carrying phoretic tarsonemid mites were selected for SEM micrographs. 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, five female paratypes (in parentheses), three males and five larvae (ranges). For leg chaetotaxy the number of solenidia is given in parentheses. Scanning electron micrographs were made with the aid of JEOL-JSM-6510LV SEM microscope. DIC micrographs were taken using the Carl Zeiss Axio Imager A2 compound microscope and digital Camera 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.
Setae v' of femur and (l) of genu needle-like; setae l' of tibia u', pv" of tarsus thickened, spiniform; other leg setae pointed and smooth.
Etymology -The specific epithet of the new species is derived from Latin word striatus meaning striate and refers to the presence of distinct linear microsculpture on the idiosomal tergites of the female and male.
Differential diagnosis -The female of the new species is very similar to T. triarcus Lindquist, 1969, described from North America, in having a triarcuate prodorsal shield, continuous ap3, and similar shape and position of idiosomal setae. The female of the new species differs from T. triarcus by the presence of distinct linear microsculpture on the idiosomal tergites (absent in T. triarcus), undulate posterior margin of tergite C (not undulate in T. triarcus), and by the absence of seta pv" on tarsus III (present in T. triarcus). The male of the new species differs from the male of T. triarcus by the presence of weak linear microsculpture on the idiosomal tergites (absent in T. triarcus) and presence of a short projection near the base of seta v' of femur IV (absent in T. triarcus).

REMARKS ON PHORESY OF Tarsonemus striatus n. sp.
Many of adult bark beetles with attached phoretic females of Tarsonemus striatus n. sp. were collected during this study. All phoretic mites were attached to the small area between coxae I and II of the host beetle ( Figure 11). In most cases only one individual of the phoretic mite was attached to one individual of bark beetle. Very rarely two individuals of mites were attached to one individual of the host beetle. A similar phoretic behavior was recently documented with aid of SEM microscopy for another bark beetle associate, Tarsonemus (Schaarschmidtia) bistridentati Magowski and Khaustov, 2006 phoretic on sixtoothed spruce bark beetle Pityogenes chalcographus L. in western Siberia (Khaustov et al. 2016).