Two new species of microdispid mites (Acari: Heterostigmata: Pygmephoroidea) associated with Lucanus ibericus (Coleoptera: Lucanidae)

Two new species of the microdispid mites (Acari: Microdispidae) phoretic on Lucanus ibericus are described from Iran: Premicrodispus gorganiensis Rahiminejad and Seyedein sp. nov. and Neomicrodispus lucani Rahiminejad and Seyedein sp. nov. The mites were collected from forests with Hornbeam trees (Carpinus spp.) and Oak trees (Quercus spp.) in Gorgan, northern Iran. The distribution of the heterostigmatic mites on lucanid beetles is reviewed. Also, a key to species of the Neomicrodispus is provided.


Introduction
Although many of heterostigmatic mites (Acari: Prostigmata) prefer to be free-living, almost all of them take advantage of phoresy in some periods of their life to distribute and establish their populations (Hermann et al. 1970;Kaliszewski et al. 1995). Heterostigmata have a wide range of associations with arthropods, including predation, parasitism and mutualism; so that different host-symbiont interactions could lead to speciation (Okabe et al. 2012). More than 2000 described species in eight superfamilies are classified in Heterostigmata (Walter et al. 2009;Zhang et al. 2011). The four families Microdispidae, Scutacaridae, Neopygmephoridae and Pygmephoridae constitute the largest superfamily in Heterostigmata (Acari: Prostigmata), known as Pygmephoroidea (Khaustov 2004). The least diverse family in the superfamily, Microdispidae Cross, 1965, includes 28 described genera and more than 120 species (Khaustov and Minor 2020) that are mostly fungivorous, inhabiting soil, litter, mosses or decaying plant material, and some are in relation with various arthropods by phoresy or parastitism with the most prevalent hosts for this family being beetles and ants (Kaliszewski et al. 1995;Walter et al. 2009;Hajiqanbar et al. 2012a;Rahiminejad et al. 2015a;Khaustov and Minor 2020). The taxonomic placement of many microdispid mites was as doubtful, hereupon, Khaustov (2018) provided a key for genera. There are various reports about microdispid mites in Iran (Rahiminejad et al. 2010(Rahiminejad et al. , 2015aHajiqanbar et al. 2012a, b;Hosseininaveh et al. 2013Hosseininaveh et al. , 2015Loghmani et al. 2014a, b;Katlav et al. 2015;Hajiqanbar and Hasseininaveh 2014;Filekesh et al. 2014;Abbasi-Moghadam et al. 2014;Badoodam et al. 2015;Azhari et al. 2018;Hajiqanbar and Arjomandi 2019;Rahiminejad and Hajiqanbar 2020). Until now, six genera and 23 species have been recorded from Iran (Hajiqanbar and Sobhi 2018).
A very diverse group of scarabaeoid beetles (Coleoptera: Scarabaeoidea), including Lucanidae, could be identified as hosts for microdispid mites (Kaliszewski et al. 1995;Walter et al. 2009;Hajiqanbar and Sobhi 2018;Khaustov and Frolov 2018). Lucanid beetles feed on honeydew or on sap from leaves and trees in their adult stage and their larvae breed in or beneath the decaying wood of logs or stumps (Holloway 2007).
During a survey on mite fauna of the cohort Heterostigmata associated with insects in Golestan province, Northern Iran, in summer 2019, two new species of the genera Premicrodispus and Neomicrodispus phoretic on beetles (Coleoptera: Lucanidae) were collected by light trap. The aim of this paper is to describe these new species. In addition, the representatives of the Heterostigmata associated with lucanid beetles are reviewed. A key for species of the genus Neomicrodispus is provided as well.

Materials and methods
Host beetles were captured by light trap in Alangdareh Forest, in Golestan province, northern Iran, during summer 2019. Mite specimens were cleared in lactophenol and mounted in Hoyer's medium. The morphology of the mites was studied by a light microscope with phase contrast illumination (Olympus BX51, Tokyo. Japan). The terminology of the idiosoma and legs follows that of Lindquist (1986), the designation of cheliceral setae follows Grandjean 1947 and the nomenclature of subcapitular setae follows Grandjean (1944). All measurements in the descriptions are given in micrometers (μm) for the holotype and four paratypes (in parentheses). Details of geographical position were recorded using a global positioning system (GPS model: eTrex).
The beetle host was identified by the help of a key for Iranian lucanid beetles provided by Bartolozzi et al. (2014).

Premicrodispus gorganiensis Rahiminejad & Seyedein sp. nov.
Zoobank: 686F49BC-B7F0-409F-A406-96217D5A4CCA (Figures 1-3) Diagnosis -The new species is characterized by posterior margin of tergites C and D with a distinct median incision; setae d, e and f blunt-ended; setae e not associated with ridge; distance d-d about 1.5 times longer than seta d; seta h 1 less than 1.5 times longer than h 2 ; seta 4a absent and seta ps 2 present; tibiotarsus I with four solenidia; all dorsal setae extending posterior border of their tergites; cupuli ia and ih rhombic.
Male and larva. Unknown. Differential diagnosis -The new species is most similar to Premicrodispus spinosus Hosseininaveh & Hajiqanbar, 2015 by seta 4a absent, seta ps 2 present, seta ps 3 longer than ps 1 and seta ps 1 longer than ps 2 , setae d and f blunt-ended, but differs in having tarsi and tibiae II and III with simple setae (tarsi and tibiae II and III with spine-like setae in P. spinosus) and seta e with no linear ridge (setae e associated with a linear ridge in P. spinosus). On the other hand, the new species is similar to P. tenuisetus Khaustov, 2006 andP. novaezealandicus Khaustov andMinor, 2020 by absence of setae 4a and presence of setae ps 2 , but differs from them by setae d, e and f blunt-ended (setae d, e and f pointed in P. tenuisetus), setae e shorter than f (setae e longer than f in P. novaezealandicus and subequal with f in P. tenuisetus), setae e not associated with ridge (setae e associated with well-developed oblique ridges in P. tenuisetus), pump 3 of pharyngeal system reduced (pump3 of pharyngeal system ovate in P. novaezealandicus and P. tenuisetus), seta ps 1 two times longer than ps 2 (seta ps 1 and ps 2 subequal in P. novaezealandicus), seta ps 3 longer than ps 1 and seta ps 1 longer than ps 2 (setae ps 3 and ps 1 subequal and longer than seta ps 2 in P. tenuisetus), posterior border of tergites C and D with distinct median incision (posterior border of tergites C and D straight in P. novaezealandicus and P. tenuisetus).
Etymology -The name of the new species refers to generic name of the host beetle,

Lucanus.
Remark -This is the first record of association between Neomicrodispus mites and lucanid beetles. Previously, N. iranicus was found in a vial containing beetle Oryctes nasicornis (L.) (Col.: Scarabaeidae) in northern Iran and N. sibiriensis collected from a decaying tree stump in Western Siberia, Russia.

Discussion
Stag beetles (Col.: Lucanidae) with about 1700 species, have a worldwide distribution (Bartolozzi et al. 2014). Ten species of lucanid beetles are listed for the arthropod fauna of Iran and it seems that Lucanus ibericus is the dominant lucanid beetle in northern Iran. This beetle feeds for several (3-7) years on decaying wood of stumps and roots in its larval stage, and the adults are related with leaves, litter and trees, therefore, it could be possible that the beetles had a close association with wide range of mites in soil or on the trees (Walter et al. 2009;Harvey et al. 2011;Okabe et al. 2012;Bartolozzi et al. 2014). Mite fauna associated with Lucanidae is poorly studied. Hitherto, three orders of mites (Mesostigmata, Trombidiformes and Sarcoptiformes) have been found to be associated with the beetles (Haitlinger 2008;Walter et al. 2009). Until now, nine species belonging to five genera and two families of Heterostigmata have been recorded as phoretic on three different species of lucanid beetle, L. ibericus, Dorcus parallelipipedus (L.) and D. parallelus (Say, 1823) ( Table 1).
As N. iranicus was collected from Oryctes nasicornis (Scarabaeidae), N. sibiriensis extracted from a decaying stump and N. lucani sp. nov. found in association with L. ibericus, it seems that a range of arthropods that dwell in decaying wood habitats could be chosen as a hosts for Neomicrodispus mites. However, more investigations on the biology and life history of Neomicrodispus can clear the nature of the associations.
Presently, the genus Neomicrodispus includes three described species based only on females that could be separated by the following key.