Demodex gapperi sp. n. (Acari: Demodicidae) from the Red-Backed Vole, Clethrionomys gapperi

Abstract

A new species, Demodex gapperi, is described with notes on its biology and host relations. Y-shaped ova, larvae with dorsal fingers and long legs III, prominent legs in nymphal and adult stages, are noted as adaptations for survival in an unusual habitat, the ducts of the Meibomian glands. The mites consume cells of the duct epithelium. An incidence of 56.3% is reported, with a 70% incidence in male and 40% in female host animals. Population studies indicate a sex ratio in the mites of 1:2 and a maximum of 73 mites from one host animal. This new species was discovered in our laboratory in 1962; however, adequate specimens for accurate description have just recently become available. Since in many respects this is a unique demodicid, the description will be followed by some account of the biology of the mite and of its host relationships. One aspect of this last, the Y-shaped ovum, has already received some attention (Nutting et al., 1968). MATERIALS AND METHODS Eighty red-backed voles (27 females, 53 males) were examined for demodicids. Scrapings from 20 of these (10 females, 10 males) were examined, each for 6 body areas (eyelid, dorsal, ventral, genital, muzzle, and perianal). For the other voles, skin scrapings were examined for dorsal and eyelid areas or eyelid only. All scrapings were mounted in Hoyer's medium or examined in peanut oil or physiological saline. In a few cases complete eyelids were digested in 10% KOH, washed, centrifuged, and examined to obtain population counts. Sectors of skin from the 6 body areas, above, and from heavily parasitized animals were fixed in Bouin's solution, paraffin-embedded, cut at 8 to 10 Au and stained with hematoxylin and eosin or Mallory's triple stain. All measurements are in microns, and are given in Table I. Received for publication 8 September 1970. *Zoology Department, University of Massachusetts, Amherst, Mass. t Study supported in part by a National Science Foundation Grant GB-3516 to the senior author. $ University of Nigeria, Nsukku, Nigeria. ? Wisconsin Alumni Research Foundation, Madison, Wisconsin. Demodex gapperi sp. n. (Figs. 1-13) Description: with characters of the genus One of the largest members of the genus; one female measured 409.6. Striking sexual dimorphism, with males approximately two-thirds length of females-especially noticeable in opisthosomal length (avg male 164.3 vs. female 252.6). Males (Fig. 1): Gnathosoma slightly wider than long. Supracoxal spines (Fig. 8) small, peglike, directed anterolaterad. Pharyngeal bulb oval with subgnathosomal setae anterior (Fig. 9). Podosoma somewhat oval in outline, less than one-third total length, and wider than opisthosoma. Legs long, evenly spaced, and approximately one-half each visible from dorsal aspect. Opisthosoma over onehalf total length, gradually tapering posteriorly with rounded terminus. Opisthosomal annuli narrow, very faint anteriorly but well-marked posteriorly. Genital orifice (Fig. 10) directly over midline between legs I and II, ovoid with distinct operculum. Penis sheathed, 20.1 long, curving ventroposteriorly and with bulbous base. Anterior dorsal tubercles above and slightly anterior to legs I. Posterior tubercles in line with anterior tubercles, at mid-line of podosoma. Females (Fig. 2): Gnathosoma and supracoxal spines similar to male but slightly larger. Pharyngeal bulb and subgnathosomal setae as in male. Podosoma elongate-oval, approximately one-quarter total length, wider than opisthosoma. Legs shorter than male, evenly spaced. Opisthosoma similar to male but markedly longer. Annuli also similar but more pronounced. Vulva 22.4 long, irregular slit, opening on opisthosoma (Fig. 11) behind closed, fused epimeral plates. Ova (Fig. 3): Remarkably long (295.8), Yshaped, widest (29.9) at base between anterior prongs. Larvae (Fig. 4): Very slender, elongate. Legs I FIGURES 1-7. Anatomy of Demodex gapperi. 1. Dorsal view of male. Arrow indicates penis. X 270. 2. Ventral view of female. Arrow indicates vulva. X 270. 3. Ovum. X 270. 4. Dorsal view of larva. Arrow indicates dorsal finger. X 270. 5. Lateral view of larva, showing dorsal finger (left) and legs I, II, and III. X 270. 6. Ventral view of nymph. X 270. 7. Anterior prongs of ovum showing larval gnathosoma (arrow) in one prong. X 1,000.