Hymenoptera

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 : 206-207

Hymenoptera : bees and wasps

In addition to beetles, different Hymenoptera belonging to the suborder Apocrita are important hosts for Scutacaridae . Apocrita divide into the monophyletic subclade Aculeata (containing ants, bees and wasps) and the artificial, paraphyletic group Terebrantia/ “Parasitica”. Members of Terebrantia have only been reported as hosts of Scutacaridae in one case: Imparipes dispar has been found phoretic on specimens of Eucoilidae, Proctotrupoidea and Pteromalidae ( Ebermann et al. 2016; Annex I). On the other hand, a larger number of scutacarids (35 spp.)

is associated with different social, but also with solitary Aculeata, as will be described below.

Bees

In the superfamily Apoidea , scutacarid mites occur together with Apidae , Andrenidae , Colletidae , Crabronidae , Halictidae and Sphecidae Annex (IV) . In fact, Scutacaridae are amongst the most frequent and diverse associates of bees ( Eickwort 1994). Most of the associated scutacarids belong to the genera Imparipes , followed by Scutacarus ( Figure 10 ).

In Apidae , scutacarid mites play no large role as inquilines of the economically important honey bee Apis mellifera : only two species, Imparipes apicola and Scutacarus acarorum , have been reported from nests of honey bees, and neither of them is a frequent associate ( Banks 1914, Schousboe 1986). More scutacarids can be found as common inquilines and phoronts of bumble bees (genus Bombus ). The scutacarid acarofauna of bumble bees consists of Scutacarus 6 species, Parascutacarus indicus Baker & Delfinado, 1975 and Imparipes degenerans Berlese, 1904 (e.g. Karafiat 1959, Cross and Bohart 1969, Larsson 2007, Jagersbacher-Baumann 2015;

for other references see Annex IV). Imparipes degenerans , however, has only been reported once from Bombus and can normally be found on ants and in their nests and also in rodents’ nests. Among the Scutacarus species associated with bumble bees, S. acarorum is particularly worth mentioning as it is one of the most common “bumble bee mites” ( Chmielewski 1971),

as it performs hyperphoresy on phoretic mesostigmatid deutonymphs (e.g. Schousboe 1986)

and as it was one of the first mite species to be described in history by Goeze in 1780 ( Goeze 1780). On bumble bees, scutacarid mites can be found on the base of the forewings, on the thorax or between thorax and abdomen, and they are most frequent on hibernated queens (e.g. Chmielewski 1971, Schousboe 1986). In the nests, the scutacarids can mostly be found in the outer portions, and they are much less frequent in artificial hives than in natural nests ( Chmielewski 1971). As workers emerge constantly in bumble bee nests, the life cycles of most associated mites are expected not to be well synchronized with that of their hosts ( Okabe 2013).

Indeed, the developmental cycle of S. acarorum takes around 9 days ( Jagersbacher-Baumann and Ebermann 2013), being much shorter than that of its host.

In nests of Apidae , flower nectar, pollen, microorganisms and nest debris are present, although microorganisms and nest debris lack in honey bees ( Okabe 2013). Dead brood, provisions and parts of the debris can become moldy and then offer suitable food for saprophagous mites like Scutacaridae ( Eickwort 1994) . As there is not much substrate which can become moldy in the nests of honey bees ( Okabe 2013), this may explain the scarceness of associated scutacarids.

Solitary bees belonging to the families Andrenidae and Colletidae generally have few associated mite genera ( Eickwort 1994). However, they serve as hosts for four scutacarid species of the genus Imparipes (e.g. Eickwort 1979, Ebermann and Hall 2003, 2004, Ebermann et al. 2013; for other references see Annex IV). The two bee families offer different habitat conditions: members of Andrenidae are ground-nesting, while Colletidae nest in dead wood. Imparipes breganti and I. burgeri , which use bees of both families as hosts, are thus considered to be pronounced generalists ( Ebermann and Hall 2004, Ebermann et al. 2013).

Imparipes apicola is associated with different species of Andrenidae , but also with Halictidae , which are another family of soil-nesting and rather primitive bees that exhibit a great diversity of mite associates ( Eickwort 1979, 1994). Eickwort (1979) gives a thorough description of the life history of I. apicola inside the cells of a laboratory reared Lasioglossum host, showing that, in contrast to species associated with bumble bees (see above), the mite’s life cycle follows that of its host. Halictid bees are also hosts for 15 other Imparipes species , moreover for two Nasutiscutacarus and two Scutacarus species (e.g. Beer and Cross 1960, Delfinado and Baker 1976, Ebermann and Hall 2005; for other references see Annex IV).

Most of these scutacarids have been found phoretic on the bees, but some have also been reported from their nests. Like in Apidae , nests of Halictidae provide flower nectar, pollen, microorganisms and nest debris as potential food sources for different mites ( Okabe 2013). Accordingly, Ordway (1964) reported mites of the genus Imparipes from halictid nest cells containing pupae, near or on the fecal deposit, and Eickwort and Eickwort (1971) also found larvae of I. eickworti Mahunka in cell contents of its halictid host.

Sphecoid wasps of the families Crabronidae and Sphecidae have been identified as phoresy hosts for five scutacarids, one Archidispus ( A. sphecis Mahunka, 1977 ) and four Imparipes species (e.g. Kuhlmann 1998, Ebermann and Hall 2003, 2004, Ebermann et al.

2013; for other references see Annex IV). Among these mites, only A. sphecis ( Lang and Mahunka 1977) is exclusively known from sphecids. The reported host species build nests in different substrates like sand, mud, dead wood or stalks. After deposition of the eggs, the nests are supplied with different paralyzed insects or spiders which serve as food for the offspring ( Witt 1998). The nests probably are suitable habitats for mites as they contain enough material which could become moldy. However, no scutacarids have been reported from nests so far,

all of the reported species were phoretic on the sphecoid wasps. Lang and Mahunka (1977) described the coxal region as favored attachment site on the hosts.

Wasps

Associations between Vespoidea (exclusive Formicidae !) and Scutacaridae are extremely rare. Species of Mutilidae and Pompilidae have been found to carry phoretic specimens of Imparipes burgeri Ebermann & Jagersbacher-Baumann, 2013 ( Ebermann et al. 2013) and Scutacarus subquadratus Khaustov & Chydyrov, 2004 ( Loghmani et al. 2014). Wasps of these families build their nests in sand, are kleptoparasites of other wasps or parasitoids on halictid bees ( Witt 1998). Another scutacarid, I. haeseleri , has been reported from a member of Vespidae ( Ebermann and Hall 2003, Hall and Ebermann 2005). The respective host species, Symmorphus bifasciatus , builds its nests in stalks, reed or dead wood ( Witt 1998) and animal meat, microorganisms, nest debris and dead larvae are available as food in its nests ( Okabe 2013). Finally, Vitzthum (1927) reported random findings of S. acarorum on wasps, not without hypothesizing that these associations may be the rare results of occasional contact between wasps and bumble bees on flowers.

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.