Scutacarus acarorum (Goeze, 1780)

(Figs. 1, 3, 10, 11)

MALE. Idiosoma length 100–160, n = 5.

Gnathosoma (Fig. 1 d) extended, tube-shaped. One pair of finger-shaped solenidia, two pairs of dorsal setae ch 1 and ch 2 and one ventral pair of ventral setae su, thin, smooth, su slightly shorter than ch 1 and ch 2. One pair of short tube-like accessory setigenous structures distally.

Dorsum (Fig. 10 a). Idiosoma with four sclerotized, very finely dotted plates. Most posterior plate forms dorsal cover for genital capsule. Length of dorsal setae: v about 17, sc 1 8, sc 2 38, c 1 41, c 2 39, d 40, e 20, f 55, h 1 9. Setae v, sc 2, e, f barbed, blunt-ended, sc 1 smooth, blunt ended, c 1, c 2, d barbed, slightly pointed. h 1 spine-like, h 2 minute. Distance between dorsal setae: v–v about 12, sc 1 –sc 1 28, sc 2 –sc 2 22, c 1 –c 1 32, c 2 –c 2 78, d–d 61, e–e 43, f–f 23, h 1 –h 1 27, h 2 –h 2 27.

Genital apparatus (Figs. 3 d, 10a). Segments H and PS fused, form genital capsule. Length of genital plate (tergite H) about 51. Posterior edge of plate narrowed (ratio length: width of genital plate = 1: 0.52). Area posterior of h 1 with roundish, sucker-like structures or cavities. Aedeagus like in I. dispar .

Venter (Fig. 10 b). Sternal plates very finely dotted. Ap1 clearly sclerotized, prosternal ap continuous from ap1 to sejugal ap; ap2, sejugal ap, ap3, and ap4 complete, weakly sclerotized; ap5 strongly sclerotized; poststernal ap incomplete, between ap4 and ap5 clearly sclerotized. Length of ventral setae: 1 a about 11, 1 b 12, 2 a 11, 2 b 11, 3 a 12, 3 b 10, 3 c 9, 4 a 8, 4 b 10, 4 c 10, ps 1 3, ps 2 10. All setae smooth, short, pointed. Distance between ventral setae: 1 a –1 a about 15, 1 b –1 b 42, 2 a –2 a 19, 2 b –2 b 41, 3 a –3 a 24, 3 b –3 b 38, 3 c –3 c 62, 4 a –4 a 18, 4 b –4 b 7, 4 c –4 c 51 ps 1 – ps 1 13, ps 2 –ps 2 18.

Leg I (Fig. 11 a). Setal formula: Tr1–Fe3–Ge4–Ti6(2)–Ta13(2). Ta with one small, padded claw. Sol ω2 thick, finger-shaped, sol ω1 thin, finger-shaped, sol ϕ1, slightly club-shaped, sol ϕ2 thin, finger-shaped. Length of solenidia: ω1 about 9, ω2 21, ϕ 1 6, ϕ 2 9. Eupathidia p’, p’’ and ft’, setae u’, u’’, s, pl’’, pv’, pv’’, v’’Ge, v’’Fe and v’Tr smooth, all other setae sparsely barbed. Setae l’Ti, pl’ and pl’’ blunt, all other setae pointed.

Leg II (Fig. 11 b). Setal formula: Tr1–Fe3–Ge3–Ti4(1)–Ta7(1). Ta with two small claws and empodium. Sol ω thick, sol ω and ϕ finger-shaped; sol ω 13, sol ϕ 9. Eupathidion tc’, setae u’, u’’, pv’, pl’’, dTi, l’Ge, l’’Ge and v’Tr smooth, all other setae sparsely barbed; all setae pointed.

Leg III (Fig. 11 c). Setal formula: Tr1–Fe2–Ge2–Ti4(1)–Ta7. Ta with two small claws and empodium. Sol ϕ 9, finger-shaped. Eupathidion tc’’, setae u’, u’’, pl’’, v’’Ti and v’Tr smooth, all other setae sparsely barbed, all setae pointed.

Leg IV (Fig. 11 d, Table 1). Setal formula: Tr0–Fe2–Ge1–Ti4(1)–Ta6. Distal Ta with two adhesive pads of differing size. Tarsal setae tc’, tc’’ are longest, length tc’ about 70, tc’’ 48. Seta v”Ti spine-like, smooth, v’Fe, dTi, l’Ti, pv’, pv’’, u and pl’’ smooth, all other setae barbed, pointed. Seta u small; sol ϕ 10, thin, baculiform.

Differential diagnosis. Males of S. acarorum have typical accessory setigenous structures which separate them from the genera Archidispus, Heterodispus and Imparipes . In comparison to males of the remaining genera, S. acarorum is most similar to S. longitarsus . It differs from the latter species by being smaller (idiosoma length about 130µm in S. acarorum versus 155µm in S. longitarsus) and by possessing relatively longer dorsal setae v and relatively shorter dorsal setae e than S. longitarsus . Moreover, the setation of leg IV differs (Table 1).

Material examined. 10 males from laboratory cultures based on females collected phoretic on bumble bees; AUSTRIA: Oisnitz, 46°54'38.3"N, 15°20'56.3"E, 1981, leg. Ebermann.

Deposition of material. 2 males: Natural History Museum Vienna, Austria (NHMW 27.641); 6 males: Institute of Zoology, University of Graz, Austria ; 2 males: Museum of Natural History of the City of Geneva, Switzerland .

Remarks. The last depiction of a S. acarorum male by Schousboe (1986) is insufficient as several setae are lacking: dorsal setae sc 1, c 2, ventral ps - setae and various setae on all four legs. On tibia I, a spine-like seta (d or k?) is depicted which could not be encountered in the investigated material. Moreover, setae h 1 are thin and long in the drawings instead of being thick and spine like.