Leptinillus validus (Horn)

Peck, Stewart B., 2007, Distribution and biology of the ectoparasitic beetles Leptinillus validus (Horn) and L. aplodontiae Ferris of North America (Coleoptera: Leiodidae: Platypsyllinae), Insecta Mundi 2007 (3), pp. 1-7 : 2-5

Leptinillus validus (Horn)

Fig. 1-8

Leptinillus validus (Horn), 1872: 145 . Original genus: Leptinus . Type in MCZC, seen. Type locality: “ Hudsons Bay Region .”

Taxonomy: Hatch 1957: 17.

Redescription and morphology of adults: Hatch (1957: 17); Parks and Barnes (1955); Wood (1965).

Immatures: Bøving and Craighead (1930); Parks and Barnes (1955); Wood (1965).

Host. The primary host of the beetle is the American beaver, Castor canadensis Kuhl ( Rodentia, Sciuromorpha , Castoridae ). The beetles are ectoparasitic as both adults and larvae but apparently spend more time in the host’s lodge and off the host than on it. Records appear in surveys or summaries of beaver parasites: e.g., Erickson (1944), Lawrence and Graham (1955), and Lawrence et al. (1961). It is of interest that no records were found in the extensive study of Janzen (1963) on the other beaver beetle, Platypsyllus castoris Ritsema , near Hastings, Minnesota. Most specimen labels do not actually cite beavers as the host. Wood (1965) reports a few adults recovered from muskrats, Ondatra zibethecus (Linnaeus) ( Rodentia, Muroidea , Cricetidae ). Since muskrats are known to share beaver lodges ( Banfield 1974), a

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Pacific Northwest. The aedeagus is fully illustrated Figure 10-12. Aedeagus of Leptinillus aplodontiae : here for the first time (Figs. 10-12). specimen from Wawona, Yosemite National Park, Biology and ecology. Unknown. California. 10) Dorsal view. 11) Lateral view. 12) Ventral view. Scale line = 0.1 mm.

Distribution. There are few literature and

specimen records. Other than the species descrip-

tion, I know only of the additional published record of Spencer (1957). I have seen only 28 specimens, and they are in the following collections: CASC, CUIC, CNCI, OSUO, SMDV, USNM. The species is known only from five general localities in the following states (Fig. 9). United States. CA, OR, WA. The distribution may be as broad as that of their hosts in the Sierra Nevada and Coast ranges of California northwards to British Columbia .

Host. The only host is Aplodontia rufa (Rafinesque), 1817 ( Rodentia, Protrogomorpha , Aplodontidae ). Common names are mountain beaver, boomer, or sewellel. Mountain beaver is a misnomer for they do not live high in the mountains, are not semiaquatic (as is the common beaver), and evolutionarily have no close relationship with the beaver. There are seven subspecies, and some of these have discontinuous distributions (see Fig. 9 and Hall 1981). The animals are secretive, nocturnal, and do not hibernate or store food. They live at lower elevations in burrows in dense streamside vegetation in dense wet forests. Their burrows are under logs, stumps, and upturned roots ( Gyug 2000). The burrow is from 10-25 cm (4- 10 inches) in diameter, and may be as long as 200-300 meters.

The family Aplodontidae is the least derived or most primitive known group of living rodents, with a fossil record from the late Paleocene to the present, and may include the ancestors of all living rodents ( Korth 1994). The family was represented by several genera which were widely distributed throughout western North America in moist habitats during the early and mid Tertiary ( Shotwell 1958). This is the only surviving rodent with the primitive character of the masseter muscle attaching to the zygma bone ( Hall 1981), a feature of many Eocene rodents. The derived state of this character is a more forward muscle attachment. The kidney is also primitive, with 70% of the nephrons located entirely in the cortex. In addition, few of the other nephrons have long loops of Henle or with a thin segment ( Dicker and Eggleton 1964). These primitive kidney features prevent the animals from excreting concentrated urine (a water-conservation adaptation of most modern rodents) and explains the need of A. rufa for ready access to water, and its present limitation to the wet Pacific Northwest.

Figures

Figure 1-7. Habitus of life stages of Leptinillis validus (from Wood 1965). 1) Dorsal view of left half adult male. 2) Dorsal view (left) and ventral view (right) of adult female. 3-5) Dorsal, ventral and lateral view of pupa. 6-7) Dorsal and ventral view of third instar larva. Scale bars = 1.0 mm.

Figure 8. Dot map showing known sites of records for Leptinillus validus in North America. Dark line indicates appproximate limits of the historical range of the host, Castor canadensis (after Hall 1981). The beetle appears to only occur on beavers throughout the northern half of the distributional range of the host.