PLATYPSYLLINAE Ritsema, 1869

This small group of parasitic beetles is represented by two species in the UK. Platypsyllus castoris is a specialist beaver parasite, while Leptinus testaceus is associated with various hosts.

Introduction

This is a small subfamily of 13 species included in 4 genera:

  • Leptinillus Horn, 1882 includes two Nearctic species associated with specific hosts:

    • Leptinillus aplodontiae Ferris, 1918 is an ectoparasite of the Mountain Beaver, Aplodontia rufa (Rafinesque).

    • Leptinillus validus (Horn, 1872) is an ectoparasite of the American Beaver, Castor canadensis Linnaeus.

  • Leptinus Muller, P.W.J., 1817. Mouse Nest Beetles. More generalist ectoparasites or commensals of small mammals with 6 Palaearctic species and 4 Nearctic species. Each species has a range of hosts; in the U.S.A. 18 species of mammal have been identified as hosts. Research suggests a Palaearctic origin for the genus and an early Tertiary entry into North America via a Bering land bridge. European species are:

    • Leptinus illyricus Besuchet, 1980. Holarctic, including the U.S.A. and south-central Europe.

    • Leptinus seriatus Dodero, 1916. From Italy.

    • Leptinus pyranaeus Besuchet, 1980. From France and Spain.

    • Leptinus vaulogeri Jeannel, 1922. From Spain.

    • Leptinus testaceus Muller, P.J.W., 1817. A widespread Palaearctic and Nearctic species.

  • Platypsyllus Ritsema, 1869. Includes a single species, Platypsyllus castoris Ritsema, 1869, which has a Holarctic distribution and has recently been discovered in Britain.

  • Silphopsyllus Olsufiev, 1923. Includes a single species, Silphopsyllus desmanae Olsufiev, 1923, which is an ectoparasite of the Russian desman Desmana moschata Pallas of Western Russia.

 

All members of the subfamily are ectoparasites of, or live commensally with, mammals; Leptinus spp. have a range of hosts. All other species are specific to aquatic or semi-aquatic mammals. Members of two genera occur in Europe. The morphological adaptations for ectoparasitism are most developed in the louse- or flea-like Platypsyllus castoris. When first discovered it was not recognized as a beetle and placed in various other insect orders; it is a small species, 2-3mm long, pale grey or brown and with strongly reduced elytra exposing most of the abdomen. The front and middle tarsi are strongly curved and the hind margins of the head, pronotum and abdominal segments bear ctenida (depressed setae) which facilitate attachment to the host’s fur. Adults and larvae presumably feed on secretions and dead skin. All species are wingless and either eyeless or with reduced eyes.

Leptinus testaceus Müller, P.W.J., 1817 

Until very recently this was the only member of the subfamily to occur in the UK, it is widespread though very local throughout England and Wales but records are scattered which, given the nature of the beetle’s lifestyle, is probably not surprising. It is absent from Scotland and the Islands although Fowler gives old records from the Clyde and Forth districts. Widespread in Ireland although these records are not on the NBN.  Generally considered an ectoparasite of mammals, living on secretions, nest refuse or mites and fleas but the species may be more general in habits than this. They have been recorded in avian nests and in association with wood mice (which seem to be a favourite host), field mice, moles, rats, shrews and small mammals in general. The beetles inhabit the nests and underground runs but have also been found on dead animals and in caves among guano. Records from among and beneath rotten wood and chalk flints suggests a more independent way of lie. The species is also a well known inhabitant of the nests of various social Hymenoptera. In the nests of Formica species they are not molested by worker which either pass them by or investigate them with their antennae before ignoring them. In the nests of Bombus spp. and Vespidae it is thought that the beetles feed on pollen and honey and otherwise scavenge a living among nest debris. These observations and views are not necessarily mutually exclusive and may indicate an opportunistic lifestyle for the species. In the U.S.A. the species overwinters in the adult stage and peak infestations on the Wood Mouse have been observed in the spring and early summer suggesting a single major emergence period. They are most easily found by examining nest material or recently dead mammals.

2-2.5mm. Entirely pale yellow, broad, flattened and rather parallel-sided.  Elytra and pronotum separately convex when viewed from above. Elytra completely covering the abdomen. Upper surface with dense, backwardly pointing punctures, which tend to run into a transverse arrangement, especially on the elytra. With long, pale yellow and recumbent pubescence. Outline of head and labrum roughly semi-circular. Labrum smooth and shiny, glabrous. Without eyes. Head with a bisinuate occipital ridge which overlaps the pronotal front angles. Hind angles of head sharp and acute. Antennae long; segments 8-11 slightly widened into an indistinct club. Pronotum transverse, with sides evenly rounded and widest a little behind the middle. Lateral margins weakly edged, not visible from above. Basal margin weakly sinuate and evenly produced backwards to the right-angled hind angles. Front margin strongly curved inward medially exposing the narrow neck. Scutellum large and triangular. Elytra without striae but faint longitudinal raised lines may be seen with low lateral lighting. Evenly rounded to apex. Abdomen with 6 visible sternites. Front coxae small, rounded and not protruding. Tibiae with 2 spurs on inner side at apex. Tarsi 5, 5, 5. Front tarsal segments 1-3 equal or subequal in length. Mid tarsal segment 1 longer than 2 or 3. Hind tarsal segment 1 as long as 2 and 3 combined. Segment 4 bilobed, especially on pro-tarsi. Claws smooth and without a tooth at base.

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POLYPHAGA Emery, 1886

STAPHYLINOIDEA Latreille, 1802

LEIODIDAE Fleming, 1821

2

2

2-3mm

Platypsyllus castoris Ritsema 1869

Beaver Beetle 

This very unusual beetle is an ectoparasite, or more accurately a commensal, on beavers, it has a Holarctic distribution but is restricted to the range of its two natural hosts, in the Palaearctic region the Eurasian beaver (Castor fiber) and in the Nearctic region the North American beaver (Castor canadensis) although the latter has is also established in parts northern Europe and Russia following introductions. The Eurasian beaver suffered a long decline in Europe due to environmental abuse and hunting etc. and by the late nineteenth century was almost extinct but recent conservation efforts have re-established the species in many of its former sites and it is now making something of a comeback. It is included in the UK list from specimens found on beavers introduced to the Scottish Highlands in 2009 in an effort to establish the species. Both adults and larvae feed on dead skin and secretions and larvae may also scavenge among lodge debris, both stages occur on the hosts and both are thought to be present year-round but oviposition and pupation are thought to occur remote from the host. Mated females leave the host and lay small batches of eggs in crevices among lodge material; larvae emerge within a few weeks, depending on temperature, and are immediately very active in searching for their hosts, entering the fur and developing in the dry layers next to the skin. Fully grown larvae leave the host and pupate in a cell among soil near the top of the lodge, the adults eclose within three weeks or so and return to the host where they will remain, except for females when they oviposit. Adults are highly adapted and not likely to be confused with any other beetle, more especially as they are generally confined to the host. The larvae are more conventional; long and moderately broad with all segments distinct and separately rounded laterally, they have tiny legs with relatively large claws which allow them to cling to the host.

Adults are quite unlike any other beetles, so much so that for some time they were not recognized as beetles, they superficially resemble lice, are small, 2.0-3.0mm, flattened and elongate-oval in outline with short legs, highly modified antennae and are pale brown in colour with the head and various pronotal markings darker. The head is circular anteriorly and produced backwards along the base, it lacks eyes, is variously depressed across the vertex and has a widely sinuate comb of stiff pale setae along the base, the antennae are 11-segmented, short and widened to a pointed apex which is obscured with long setae. The pronotum is broadest at obtuse posterior angles, the anterior margin deeply cleft and the basal margin produced backwards, with tufts of long setae towards the lateral margins and strongly sinuate either side of the middle, the surface with a mixture of fine and coarse punctures and the lateral margin recessed for reception of the antennae. Scutellum large and triangular. Elytra transverse, broadest towards the apex and separately rounded apically, with scattered large punctures which are dense laterally and without striae. Hind wings absent. Abdomen with six visible sternites, curved laterally and broadest before the middle, each sternite strongly curved and with a subapical row of fine setae. Legs short and robust, coxae flat, middle and hind tibiae with strong spines externally, front tibiae with spines near the apex. Tarsi 5-segmented; all segments narrow and elongate, claws well-developed and smooth, without a basal tooth and not fused.

For an account of the species occurrence in the UK see Duff, A.G, Campbell-Palmer, R. and Needham, R 2013 The beaver beetle Platypsyllus castoris Ritsema (Leiodidae: Platypsyllinae) apparently established on reintroduced beavers in Scotland, new to Britain. The Coleopterist 22(1):9-19, April 2013.

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