Macrocheles

 

HARMFUL | NOT HARMFUL | UNCERTAIN

mostly neutral to beneficial; feeds on nematodes and small arthropods in nests; one species may be harmful, hindering bees' movements by dispersing on bees in large numbers

Name and classification

Macrocheles Latreille, 1829

Taxonomy
Superorder Parasitiformes » Order Mesostigmata » Suborder Monogynaspida » Hyporder Dermanyssiae » Family Macrochelidae » Genus Macrocheles

Type species
Acarus marginatus Hermann, 1804 (=Acarus muscae domesticae Scopoli, 1772) by subsequent designation.

Common names
house fly mite, referring to the most common and cosmopolitan species, Macrocheles muscaedomesticae, which usually disperses on flies.

Diagnosis

Female: With accessory sclerites beneath lateral margins of epigynal shield (Fig. 2). Peritreme looped proximally, joining the stigma posteriorly (Fig 6). Well-developed arthrodial brushes present on chelicerae (Fig. 7). Claws and ambulacra on leg I absent but present on tarsi II-IV (Figs. 1, 2). 2-3 pairs of opisthonotal dorsocentral setae (J2, J5 or J1,J3, J5) (Fig 3). Sternal shield without strongly raised reticulate ornamentation and not strongly enclosing genital shield (Fig. 5). Ventrianal shield with 3 pairs of setae (JV1, ZV2-3) plus 3 circumanal setae (Figs. 2, 4).

Species identification

This is a species-rich genus that includes 15 bee-associated species. Dichotomous keys are not available. Keys to Palaearctic species (Karg, 1971; Bregetova, 1977d) can be used as a starting point. Other important works include papers on Macrocheles associated with bumble bees in North America (Richards and Richards, 1977) and Apis dorsata in Indonesia (Hartini et al., 2013).

Similar genera

In Glyptholaspis—three species of which have been found in beehives—dorsal shield strongly crenulate-reticulate and sternal shield extending posterolaterally around epigynial shield to the level of the posterior angles of coxae III and abutting rounded metasternal shields. In Macrocheles, dorsal shield smooth, punctate, reticulate, or areolate; sternal shield not extending posterolaterally to the level of the posterior angles of coxae III; metasternal shields rounded or elongate, separated from, or abutting, posterolateral angles of sternal shield.

In addition, two other genera, Holostaspella and Neopodocinum, were recently found in nests of the giant honey bee, Apis dorsata (Hartini et al., 2013). Species in these genera are habitat generalists. They can be separated from Macrocheles using available keys in Krantz, 1962.

Distribution

Cosmopolitan. Species associated with bees have been collected in the Nearctic, Palaearctic, Neotropical, and Australian regions.

Bee hosts

bumble bees (Bombus), honey bees (Apis), and a stingless bee, Melipona

Host association level

Permanent

associated exclusively with bees or their close relative, wasps; cannot live without these hosts

Temporary

some life stages are associated with bees, while others are not

Facultative or opportunistic

can complete entire life cycle without bees or their close relative, wasps

Most generalist species are facultative.

Macrocheles praedafimetorum and M. rotundiscutis, species associated with bumble bees, are intermediate between facultative and permanent.

Host associations, feeding, and dispersal

Most species (habitat generalists)

  • All stages live in a variety of habitats (manure, dung, litter, decaying organic substances, and nests of social bees), where they feed on small invertebrates.
  • Female mites, and occasionally protonymphs and deutonymphs, disperse on adult insects, including bees.

Species associated with bumble bees (M. rotundiscutis and M. praedafimetorum)

  • All stages live in nests of bumble bees (Bombus spp.) or, less frequently, other habitats, where they feed on small invertebrates without causing any harm to the hosts.
  • Female mites disperse on dung-inhabiting beetles that are attracted to bumble bee nests by the decaying material on the bottom of the domicile.

Biology

Species of the genus Macrocheles are common predators of nematodes, oligochaetes, and the eggs and larvae of small insects and mites in a wide range of organic substrates, such as animal dung, hay, rotting stumps, galleries of bark beetles and subcortical situations, and nests or galleries of mammals, birds, and social insects, including bees (Bombus, Apis, and Melipona). These mites commonly form phoretic associations with beetles and flies to colonize fresh substrates. Typically, only inseminated females disperse, although protonymphs and deutonymphs of the Macrocheles dimidiatus species group have also been found to be phoretic.

Among mites found on bees and/or in their nests, there are two very similar species from bumble bees (Bombus spp.): Macrocheles rotundiscutis (=M. bombophilus) from Europe and Macrocheles praedafimetorum from North America. These species have a clear preference toward bumble bee nests, although they can be found in other habitats. In nests of bumble bees, the mites often reach large population sizes, feeding on a wide range of saprophagous organisms common to dung and decaying matter, without any negative effect to the hosts. Cannibalism has also been recorded. It is interesting that dispersal does not occur on bumble bees, but on a dung-inhabiting beetle that is apparently attracted to bumble bee nests by the decaying material on the bottom of the domicile (Richards and Richards, 1977).

In contrast, species reported from hives of honey bees (Apis spp.) and other social bees are habitat generalists that can probably also use bees as transport (Chmielewski, 1991a; Grobov, 1978).

Because Macrocheles species may consume harmful microarthropods in bee nests, they can be beneficial to their hosts. Predation on the bee brood is unlikely. Macrocheles may be somewhat harmful if large numbers of mites disperse on a single adult bee. For example, a single adult bee may carry up to 30 females of M. glaber (Vitzthum, 1926). In this relatively uncommon case, the bees' movements can be hampered (Homann, 1933).