Coleoptera

Baumann, Julia, 2018, Tiny mites on a great journey - a review on scutacarid mites as phoronts and inquilines (Heterostigmatina, Pygmephoroidea, Scutacaridae), Acarologia 58 (1), pp. 192-251 : 203-206

Coleoptera

In the taxon Coleoptera , by far the most scutacarid species (62 spp.) can be detected on ground beetles, Carabidae Figures (8-9; Annex II). All of the mites associated with Carabidae belong to the genus Archidispus , no other scutacarid genera have been found so far (e.g. Karafiat

1959, Kurosa 1977, 1980, 1989, 2005, Khaustov 2008; for other references see Annex II).

Moreover, Archidispus can only rarely be seen on beetles belonging to families other than

Carabidae . Only two species, A. armatus and A. bembidii , can apart from Carabidae also be encountered on Heteroceridae , Hydrophilidae and Staphylinidae ( Karafiat 1959, Mahunka

1972b, Khaustov 2008), and A. irregularis Katlav & Hajinqanbar, 2016 was found only on

Staphylinidae . Generally speaking, different scutacarid genera can be found on other beetle families, but among them, the genus Scutacarus is the most prominent ( Figure 10 ).

In the following, the beetle families reported to be hosts for scutacarids will be discussed.

Within the family Carabidae , most associated Archidispus species are rather opportunistic regarding their host choice: the majority of the reported species have been found on different species of one carabid genus, and about the half of the scutacarids occurred on several different carabid genera. The scutacarids have only been reported from imagines, they have never been found on the beetles’ soil living larvae or pupae ( Karafiat 1959). On their carabid hosts, the mites can be found on four typical attachment locations: the cervical membrane between head and prothorax, the intersegmental membrane between pro- and mesothorax, between thorax and abdomen, and finally under the beetle’s elytra (e.g. Karafiat 1959, Kurosa 1970, 1972 a,

Khaustov 2008). Some Archidispus species show no preference for special attachment sites

( Kurosa 1984), while others prefer certain regions. For example, A. magnificus preferably attaches on the anterior part of the prothorax of its carabid hosts and A. sugiyamai Kurosa,

1991 on the posterior part of the prothorax ( Ebermann et al. 2011). These two species can also simultaneously be found on the same host, each one on its preferred attachment site. It is common to encounter more than one Archidispus species on one host (e.g. Kurosa 2009). Only five Archidispus species found on Carabidae have also been reported from soil samples, and all of them display phoretomorphism ( Table 1). The carabid beetles used for phoresy usually occur in moist environments, which are often inhabited by scutacarid species as they favour the growth of fungi. The moist habitats don’t offer stable environmental conditions as they are prone to frequent flooding, and thus the respective scutacarids strongly depend on phoresy in order to escape from flooded regions ( Ebermann 1991a).

Additional to Carabidae , scutacarids in moist habitats also use ripicolous Heteroceridae and Hydrophilidae as hosts (Annex III). On these two beetle families, species belonging to the genera Archidispus , Imparipes , Pygmodispus and Scutacarus can be found ( Karafiat 1959, Kurosa 1980, Messner 2001, Khaustov 2008, Ebermann et al. 2016). The respective mites have been reported from under the elytra or attached randomly on the beetles’ surface ( Karafiat 1959).

Members of Staphylinidae also often occur in moist habitats, moreover on dung and on carcasses ( Zahradník 1985). Mites belonging to five scutacarid genera have been found phoretic on staphylinid beetles from the Holarctic and from Sudan: Archidispus armatus , A. irregularis , Imparipes dispar , I. histricinus , Lamnacarus ornatus and 3 Scutacarus species (e.g. Karafiat 1959, Ebermann 1991 a, Khaustov 2008, Truck 2012, Ebermann et al. 2016; for other references see Annex III). Most of these scutacarid species have also been recorded from other habitats like soil, moss, manure or Fragaria plants. On their host, the mites can be found rather randomly on different attachment sites like the legs, the lateral abdomen or between caput and prothorax ( Karafiat 1959, Ebermann 1991a).

Scutacarids can also be found on beetle families which occur in other than moist habitats which may be suitable for the mites as well: fungus-infested wood, manure, carcasses and different types of decaying material in general.

Beetle species with an affinity to fungus-infected wood can be found in the families Curculionidae and Cupepidae (Annex III). In Curculionidae , Scutacarus scolyti Mahunka

& Moser, 1980 and S. cf. culmusophilus Sevastianov, 1975 have been reported from four species of wood borer and bark beetles from Eurasia ( Mahunka and Moser 1980, Khaustov 2008, Knapp 2008). The mite occurs in the galleries made by the beetles ( Khaustov 2008) and also phoretic on setae on the base of the coxae ( Mahunka and Moser 1980). As the galleries made by these beetles are known to contain fungi (e.g. Vega & Blackwell 2005, Okabe 2013),

it is probable that the scutacarids feed on them. Moreover, dead wood and microorganisms are available as possible food sources ( Okabe 2013). The red palm weevil Rhynchophorus ferrugineus is another curculionid beetle which has been reported as host for a not nearer identified species of the genus Scutacarus in Egypt ( El-Sharabasy 2010). The beetle is an important pest of palms in Asia and Europe which is known to be a host to several mite species ( Al-Deeb et al. 2011), but associated scutacarids had never been reported before.

One species of Cupepidae, the North American Tenomerga cinerea , has been given as host of the scutacarid Imparipes cupes Delfinado & Baker, 1978 ( Delfinado and Baker 1978). Larvae of T. cinerea are known to thrive in fungus-infested wood ( Hörnschemeyer 2005),

which probably is a suitable habitat for the scutacarids as well.

Scarabaeidae , which often are coprophilous and as such visit habitats that are commonly used by scutacarid species, have also been reported as phoresy hosts for several scutacarids: Archidispus sacculiger (Mahunka, 1968) , Heterodispus near elongatus (Trägardh, 1904) , two Pygmodispus species and three Scutacarus species have been found phoretic on Scarabaeidae from Brazil, Canada, Chile, Iran, Java and the USA ( Paoli 1911, Mahunka 1968 a, Norton 1973, Ebermann and Rodrigues 2001, Rodrigues et al. 2001, Ebermann et al. 2003, Loghmani et al. 2014; Annex III). Not all of the scarabaeid species used as hosts are dung beetles: imagines of Osmoderma eremicola feed on sap and damaged fruits, but the juvenile stages thrive in decaying wood ( Norton 1973), and the juveniles of Bothynus striatellus are crop pests in South America (SiNAViMo 2015). As attachment sites on the beetles, the underside of the elytra, hairs on the ventral side and the suture between forelegs and head have been reported ( Mahunka 1968a, Ebermann and Rodrigues 2001, Ebermann et al. 2003).

Another family of beetles occurring in different types of decaying material is the family Ptiliidae . These mycophagous beetles are characterized by very small body sizes ( Zahradník 1985), still three different Scutacarus species have been reported from one single specimen of Ptiliidae which has not been identified to genus- or species level ( Mahunka and Zaki 1992, Truck 2012; Annex III). The mites attach to thick hairs on the abdomen or legs of the beetles ( Truck 2012).

Members of the family Tenebrionidae also are used as hosts by scutacarids (Annex III). Beetles of this family are generalists ( Zahradník 1985), and thus it is very likely that they often visit habitats that are suitable for scutacarids, too. Two Heterodispus species from Ukraine and Africa have been reported phoretic on tenebrionid beetles, whereas the concrete attachment sites are unknown ( Khaustov 2008, Jagersbacher-Baumann and Ebermann 2012a).

The last family of Coleoptera which has been reported as host for Scutacaridae is the

Pselaphidae . Only one scutacarid species phoretic on Pselaphidae is known to date, namely

Imparipes pselaphidorum Ebermann, 1988 from individuals of the genus Centrophthalmus in

Tanzania (Ebermann 1988; Annex III). Many Pselaphidae are known to be myrmecophilous

( Zahradník 1985), which could be an explanation for why the scutacarids can be found on with them: the mites could be primarily commensals of ants which also can move to the syntopically occurring beetles. However, the pselaphids found to bear I. pselaphidorum are not myrmecophilous and thus the reasons for the associations between mites and beetles remain unclear (Ebermann 1988).

Finally, there are also reports of scutacarid mites phoretic on not nearer identified

“coleoptera” from Australia and Ghana (Annex III). They comprise Archidispus cornutus

(Mahunka, 1973), Diversipes horridolatus Mahunka, 1975 , Lamnacarus expansus Mahunka,

1973, 2 Scutacarus species , 3 Symbolacrasis species and two species of Thaumatopelvis

( Mahunka 1973a, 1973b, 1975c, Ebermann 1980b). The three species Symbolacrasis acutimera Mahunka, 1973 , S. hypostigma Mahunka, 1973 and S. synmixta Mahunka, 1973 are the only known members of Symbolacrasis, which means that the entire genus is known exclusively phoretic on coleopterans.

Figures

Figure 10 Number of scutacarid species belonging to different genera associated with bees and wasps (Apoidea and Vespoidea excl. Formicidae). “Other genera” combineDiversipes, Lamnacarus, Lophodispus, Nasutiscutacarus, Parascutacarus, Reductacarus, Rettenmeyerella, Scutacaropsis, SymbolacrasisandThaumatopelvis.