Macrocheles kekensis sp. n., a new macrochelid mite associated with a centoniin beetle from Hungary (Acari, Mesostigmata)

Abstract A new species, Macrocheles kekensis sp. n., is described based from three specimens associated with a cetoniin beetle (Hoplia hungarica Burmeister, 1844). The new species differs from the other known European macrochelid species in having 29 pairs of dorsal setae, j1 and z1 short and robust, other dorsal setae long and pilose, and the absence of apodemes between the genital and ventrianal shields. This is the 34th Hungarian macrochelid species.


Introduction
Members of the mite family Macrochelidae (Parasitiformes: Mesostigmata) are large, fast-moving predators inhabiting soil substrates, litter and decomposing organic matter. The macrochelids feed on nematodes, eggs and larvae of insects or weakly sclerotized mites, and very often live in association with certain insect groups (e.g. flies and beetles) (Mašán 2003). Macrochelidae is relatively well known in some Central European countries like Germany (Karg 1993), Austria (Johnston 1970) and Slovakia (Mašán 2003). However, information about their occurrence in Hungary is insuffi-cient, although numerous records were presented over the past 20 years (e.g. Ács and Kontschán 2014, Kontschán 2005, 2015, 2015a, 2015b, 2016, Salmane and Kontschán 2005. Only a few beetle-associated macrochelids have been mentioned (Kontschán 2006) from Hungary, while macrochelid mites associated with centoniin beetles are rarely collected. The association of macrochelid mites with flower beetles seems to be a rare phenomenon. Mašán (2003) in his monograph about the macrochelid mites of Slovakia mentioned only four species associated with a centoniin species (Potosia cuprea Fabricius, 1775).
The subfamily Cetoninae is a very species-rich group in Hungary (Enyedi 2006), majority of the species can be observed on the flowers of the plants in summertime. So far only one species [Macrocheles glaber (J. Müller, 1860)] has been reported from Cetonia aurata from Hungary . Recently, some macrochelids were collected on a Hoplia hungarica Burmeister, 1844 beetle (Scarabaeidae: Cetoniinae), which are described as a new species here.

Materials and methods
The three mite specimens were collected as phoretic individuals on a Hoplia hungarica Burmeister, 1844 beetle in the eastern part of Hungary. The host beetle was attracted to a lamp of the house and was found on the ground close to the house wall. The specimens assigned here to the new species (n = 3, females) were collected from the body of the host beetle using a brush observed under a BTC binocular microscope. Later they were cleared in lactic acid and were placed on a slide with deep cavity for examination. Drawings were made with the aid of a drawing tube on a Leica 1000 microscope. All specimens are stored in 75% ethanol and the holotype and one paratype are deposited in the Natural History Museum, Budapest, plus one paratype in the Natural History Museum in Geneva. Measurements are presented in minimum and maximum size. Measurements and the scales in the figures are given in micrometers (μm). The new species was also tested using the keys provided by Bregetova (1977), Karg (1993) and Mašán 2003.
Material examined. Holotype. Female. Collected from Hoplia hungarica Burmeister, 1844 Hungary, Kék village, 48°06'38"N, 21°52'51"E, 10 m a.s.l., 05 May 2017. Kontschán, J. coll. Paratypes. Two females, locality, date and host same as for holotype. The holotype and one paratype were deposited in the Soil Zoology Collections of the Hungarian Natural History Museum, Budapest, the other paratype in the Arachnida collection of the Natural History Museum, Geneva, Switzerland.
Etymology. The name of the new species refers to the village (Kék, East-Hungary) where the species was collected.

Remarks
The short, robust, and small setae j1 and z1 are present in numerous macrochelid mites distributed in Europe, but the majority or all dorsal setae are smooth in these known species, contrary with new one, where only the latter mentioned two pairs of setae are smooth and the others are marginally pilose. Macrocheles subbadius (Berlese, 1904) and Macrocheles insignitus Berlese, 1918 have similar ornamentations on sternal and ventral shields and have short and robust j1 setae, but these two species have smooth setae on dorsal shield, which are pilose in the new one.

Discussion
The systematic position of the new species is questionable. The serrate dorsal seta on chelicerae are a distinctive character of the genus Nothrholaspis, but members of the genus Nothrholaspis has three pairs of small apodemes between genital and ventrianal shields and tectums are forked to lateral and central branches (Emberson 2010, Babaeian et al. 2014, Özbek and Bal 2013. The dorsal seta of the chelicera of the new species is apically serrate, which matches the diagnosis of the genus Nothrholaspis. However, the apodemes are missing in the new species and the shape of tectum is also different. Due to the shape of tectum and the absence of apodemes between the genital and ventrianal shield, I cannot place the new species into the genus Nothrholaspis, therefore it is temporarily placed in the genus Macrocheles sensu lato.
The host species (Hoplia hungarica) is a rare beetle found in Hungary. Usually only one or two localities are mentioned in faunistic studies (Ádám 1997, Enyedi 2006, Rozner 2001. Therefore the finding of the macrochelid mite on this infrequently collected beetle was absolutely unexpected.