Gamasodes queenslandicus Halliday & Walter, 2005

Halliday, R. B., Walter, D. E. & Polak, M., 2005, A new species of Gamasodes Oudemans from Australia (Acari: Parasitidae), Zootaxa 1001 (1), pp. 17-30 : 18-27

Gamasodes queenslandicus Halliday & Walter sp. nov. ( Figs. 1–13 )

Material Examined

Holotype: deutonymph, Australia, Queensland, Cape Tribulation , January 2003, on Drosophila sp. , M. Polak coll. ( ANIC) . Paratypes: 17 DN, 2 males, same data as holotype; 43 DN, 6 males, 3 females, Cincinnati USA, in lab culture of Drosophila sp. , origin Cape Tribulation, removed from culture 9 May 2003, M. Polak coll. ( ANIC) ; 2 DN, Cape Tribu­ lation, Gray's Fruit Farm, 9 October 2001, on Drosophila bipectinata, M. Polak coll. ( ANIC) ; 9 DN, Iron Range , 14 km ENE of Mount Tozer, July 1986, dung­baited trap (human faeces), T. Weir ( ANIC) ; 3 females, 2 males, 2 DN, Mossman Gorge (16°29’S, 145°20’E), Daintree National Park, 31 January 1996, ex rotting fungi, D. E. Walter; 4 DN, same data except phoretic on tipulid fly reared from fungi, D. E. Walter. ( UQIC) .

Description

Deutonymph

Dorsal idiosoma ( Fig. 1 ). Length 538–559 µm, width (at posterior margin of podonotal shield) 365–399 µm. Podonotal shield with anterior and lateral polygonal ornamentation, centrally smooth; with 20 pairs of setae; j1 long, thick (37 µm) with very slight distal pilosity, distance between insertions approximately equal to length of setae; z1, s1, s2 minute, j4, r3, z5 very long and thick (58 µm), distally pilose, others smooth and pointed, 29–32 µm; r2 and r4 minute, inserted in soft lateral integument. Opisthonotal shield with polygonal ornamentation throughout, with 12 pairs of setae, Z1, Z3 very long, thick, distally pilose (52–63 µm), others shorter, smooth and pointed (30–42 µm).

Ventral idiosoma ( Fig. 2 ). Tritosternum with elongate rectangular base and lightly pilose laciniae. Pre­sternal region with two pairs of plates, comprising a large trapezoidal inner pair and a smaller crescent­shaped outer pair. Sternal shield with irregular outline, with a narrow posterior extension at the level of coxa IV; with polygonal ornamentation throughout, and with four pairs of smooth pointed setae and three pairs of pores. Endopodal plates between coxae II and III transversely oriented, with irregular inner margins. Peritremes extending from just anterior to coxae I to level with the anterior margin of coxae IV. Opisthogastric integument with eight pairs of smooth pointed setae, the one immediately behind coxae IV minute, and a pair of irregular oval­shaped metapodal plates. Anal shield trapezoidal, cribrum very small, anus situated near posterior end of shield; para­anal and post­anal setae smooth and pointed, subequal in length.

Gnathosoma . Subcapitulum ( Fig. 3 ). Deutosternal groove with 10 transverse rows of denticles, ca. 15 denticles per row. Hypostomal setae h1, h3, and palp coxal seta subequal in length (40–50 µm), h2 shorter (ca. 30 µm). Corniculi curved and robust, reaching to mid­level of palp femur. Internal malae long and ribbon­like, external malae forming a broad fringe. Chelicera ( Fig. 4 ). Fixed digit with five triangular teeth and pilus dentilis; movable digit with a large triangular proximal tooth and two smaller distal teeth; arthrodial brush short. Epistome ( Fig. 5 ) an irregularly serrated arch with ca. 12–15 points, median point somewhat more prominent than lateral serrations, details variable among specimens.

Legs. Chaetotaxy: Leg I: coxa 0 0/1 0/1 0, trochanter 1 1/1 0/2 1, femur 2 2/3 3/1 2, genu 2 3/2 3/1 2, tibia 2 3/2 3/2 2. Leg II: coxa 0 0/1 0/1 0, trochanter 1 0/1 0/2 1, femur 2 3/2 2/1 1, genu 2 3/1 2/1 2, tibia 2 2/1 2/1 2, tarsus 3 3/2 3/2 3 + mv, md. Leg III: coxa 0 0/ 1 0/1 0, trochanter 1 0/1 0/2 1, femur 1 2/1 2/0 0, genu 1 2/1 2/1 2, tibia 2 2/1 2/1 1, tarsus 3 3/2 3/2 3 + mv, md. Leg IV: coxa 0 0/0 0/1 0, trochanter 1 0/1 0/2 1, femur 1 2/1 2/0 0, genu 2 2/1 3/1 1, tibia 2 1/1 3/1 2, tarsus 3 3/2 3/2 3 + mv, md. Setae av 1, av 2 on femur I, av 1 on genu I, and a v 2 on tarsus II modified to thick blunt spines inserted on cuticular protrusions, av 1 on tarsus II greatly expanded, long and sword­like, all other setae fine, smooth, pointed, basifemur I with a blunt non­setose ventral spur ( Fig. 6 ).

Adult female

Dorsal idiosoma ( Fig. 7 ). Dorsum covered by two shields weakly united medially. Podonotal region (463–500 µm long, 535–600 wide) roughly reticulate anteriorly, smooth medially, and with postero­lateral polygonal ornamentation with punctate angles; with 20 pairs of setae, most (j2–3, 5, 6; z1–4, 6; s1–6; r5) simple, acicular; j1 (60–70 µm), j4 (62– 73 µm), z5 (73–78µm), and r3 (85–105 µm) thickened and distally pilose; plicate cuticle laterad shield with five pairs of simple r setae, r2 and r4 inserted near margin of shield. Peritrematal shield broad and fused to podonotal region at anterior margin; peritremes linear and reaching to about the level of setae z1. Opisthonotal region 400–460 µm long, 540–580 wide, with polygonal ornamentation and punctate angles throughout, with 15 pairs of setae, most (J1–5; Z2, 4, 5; S1–5) simple, acicular; Z1 (75–88 µm), Z3 (75–86µm) thickened and distally pilose; plicate cuticle laterad shield with about 24 pairs of simple setae.

Ventral idiosoma ( Fig. 8 ). Tritosternum with columnar base (37–55 µm high) and completely separate pilose laciniae (83–95 µm long). Pre­sternal region with one pair of plates. Sternal shield well developed and fused to endopodals I–II, with weak punctatereticulate ornamentation, three pairs (st1–3) of smooth pointed setae and two pairs (stp1– 2) of lyrifissures, posterior margin with deep median notch that receives the metasternal shields, and a pair of shallow lateral notches. Metasternal shields large and angular, fused to endopodals III–IV and bearing simple st4 and stp3. Posterior acetabulum of leg IV with strap­like parapodal plate bearing three inguinal gland openings. Opisthogaster covered by a single hologastric shield with eight pairs of setae, punctate­reticulate ornamentation, and fused to the peritrematal shields; genital region mucronate, with simple setae st5 inserted at the level of a band of thin cuticle; JV1–5 and ZV1–2 simple, acicular; JV5 stout, distally pilose, and inserted caudally; anal opening raised, flanked by simple para­anal setae (ca 30 µm long) and simple, slightly shorter post­anal seta; cribrum terminal. Endogynium weakly sclerotized, barrel­shaped, with faint reticulate ornamentation, each polygon with numerous small internal punctures.

Gnathosoma . Subcapitulum ( Fig. 9 ). Deutosternal groove with 11 transverse rows of denticles, anteriormost smooth or with a few denticles, rows 2–9 with numerous irregular teeth, rows 10–11 smooth. Palp coxal seta (43–50 µm) and hypostomal setae simple and acicular, h3 longest (90–95 µm long), h2 shortest (29–38 µm). Corniculi horn­like (78–82 µm along outer margin), not grooved dorsally, reaching to mid­level of palp femur. Chelicera ( Fig. 10 ). Fixed digit with five triangular teeth and spine­like pilus dentilis; movable digit with a large triangular proximal tooth and two smaller distal teeth; arthrodial brush short. Epistome ( Fig. 11 ) with short median mucro and irregular lateral simple or bifurcate denticles. Palp. Setation of trochanter, femur, genu and tibia 2­5­6­14, respectively; distal seta of trochanter distally barbed; femur with anterolateral and dorsal seta distally expanded and barbed; both anterolateral setae of genu distally spatulate.

Legs. Chaetotaxy: Setal complement and arrangement as in DN; setae av 1, av 2 on femur I and av 1 on genu I modified to thick blunt spines inserted on cuticular protrusions, seta av 1 on genu II somewhat thickened, but not spur­like; ventral setae of tarsus II not modified; some dorsal setae sparsely pilose distally.

Adult male

Idiosoma. Similar to female except in sterno­genital region and with more extensive sclerotization; holodorsal shield 735–865 µm long; holoventral shield with large (70–85 µm across) genital opening at base of small tritosternum (55–65 µm long).

Gnathosoma . Similar to female except for chelicerae and hypostomal seta h1. Chelicerae 320–358 µm long; movable digit (108–115 µm) with single tooth at distal extremity of paraxial, ridge­like spermatotreme; fixed digit 220–230 µm long with distal offset tooth, 15–20 minute serrations, and two large teeth ( Fig. 12 ). Hypostomal seta h1 (77–99 µm long) much thicker than h3 (83–93), h2 short (33–38), palpcoxal seta intermediate (38–50).

Legs. As for DN except femur II with a large ventral spur (rising 50–55 µm) bearing button­like av1 at its tip, and axillary av2 sessile, button­like, both with striate surfaces; genu and tibia II each with av1 button­like with striate surface, heavy spine­like setae absent ( Fig. 13 ).

Notes

Previous knowledge of Gamasodes would suggest that it is a Palaearctic/Oriental genus, with a single species in Madagascar (see Appendix). The discovery of a species in Queensland shows that the genus is more widespread than previously realised.

Most species of Gamasodes are known only from the deutonymph. The deutonymph of G. queenslandicus may be distinguished from other species of Gamasodes by the fact that dorsal idiosomal setae j4, r3, z5, Z1, Z3, J5 are long, thick and distally pilose, while all other idiosomal setae are fine, smooth and pointed. No other species in the genus has this combination of character states. G. assamensis Bhattacharyya , G. bulgatus Athias­ Henriot and G. nudus Tseng are known only from the adult female. The adult female of G. queenslandicus may be distinguished from these species by the lack of notches in the anterior margin of the sternal shield, and the distinctive shape of the metasternal shields. Two European species, G. ignoratus Oudemans and G. poppei Oudemans , are insufficiently known and cannot be recognised.

Deutonymphs of G. queenslandicus demonstrate sexual dimorphism typical of the Parasitidae , as described by Wrensch & Johnston (1983). Female deutonymphs have a small nodular marking in the posterior half of the sternal shield, from which reticular markings radiate in a star­like pattern. In samples of specimens collected from the field at Iron Range and Cape Tribulation there were 19 female and 10 male deutonymphs. The sex ratio in deutonymphs from laboratory culture was also somewhat female­biased, at 25 females and 13 males.

Biology and behaviour

The specimens described here were encountered during studies of the population biology of fruit­inhabiting Drosophila bipectinata ( Polak et al., 2004) and of acarine species diversity ( Walter & Proctor, 1998) in north Queensland. Mites were found attached to the ventral abdominal surface of a tipulid fly emerging from rotting fungal sporocarps, and on fruit flies of both sexes. The maximum number of mites observed attached to one fruit fly was two (n = ca. 25 flies). Mites were also found attached to other Drosophila species occurring on jackfruit, and walking on the exposed tissue of the fruits. Collections from fruit flies, fruit, rotting fungi, and dung­baited traps suggest that G. queenslandicus is a generalist in both the resources it uses and in its phoretic carriers.

Mites attach to and penetrate the integument of Drosophila with their mouthparts, causing 'scar' formation at the site of attachment. Scars are small darkened (melanized) areas of encrusted fly haemolymph that seeps from the mite­inflicted wound. The scars caused by G. queenslandicus are similar to those inflicted by another mite, Macrocheles subbadius (Berlese) , on the North American fruitfly D. nigrospiracula Patterson & Wheeler ( Polak, 1996) . M. subbadius is normally a predator ( Axtell, 1961) but causes reductions in both survival and fecundity of D. nigrospiracula when attached. Wade & Rodriguez (1961) also noted that Macrocheles muscaedomesticae was capable of sucking the bodily fluids of adult house fly Musca domestica , as well as preying on its eggs and larvae. By analogy, it appears that G. queenslandicus may consume haemolymph while attached to D. bipectinata , and should be considered an opportunistic parasite of Drosophila and not simply phoretic. Although these mites depend on their hosts for transport to the patchy habitats in which they develop (e.g. fruit, dung, fungal sporocarps), they use a variety of insect hosts. Negative effects on host species have been shown to be more likely to occur when parasites have alternative carriers ( Herre, 1993).

In parasitids only the deutonymphal stage is phoretic (e.g. Krantz, 1983), in contrast to M. subbadius , where only the adult female mite is phoretic and/or parasitic. Although the deutonymphal stage of G. queenslandicus may display a degree of parasitism, the other stages of the life cycle are free­living predators. Many of the mites examined in this study were obtained from a laboratory culture in which they were feeding on nematodes. When this culture was established, the mite’s population size increased dramatically, and the culture was maintained continuously on a diet of nematodes from February 2003 to December 2004. The life cycle strategy of these mite species is therefore a mixed one, including both predation and parasitism.

Figures

FIGURE 1. Gamasodes queenslandicus sp. nov., deutonymph. Dorsal idiosoma. Scale bar = 100 µm.

FIGURE 2. Gamasodes queenslandicus sp. nov., deutonymph. Ventral idiosoma. Scale bar = 100 µm.

FIGURES 3–6. Gamasodes queenslandicus sp. nov., deutonymph. 3. Hypostome, 4. Chelicera, 5. Epistome, 6. Femur and genu of leg II. Scale bar = 100 µm.

FIGURE 7. Gamasodes queenslandicus sp. nov., Female dorsal idiosoma. Scale bar = 100 µm.

FIGURE 8. Gamasodes queenslandicus, sp. nov. Female ventral idiosoma. Scale bar = 100 µm.

FIGURES 9–13. Gamasodes queenslandicus, sp. nov. 9. Hypostome of female, 10. Chelicera of female. 11, Epistome of female. 12, Chelicera of male. 13 Femur, genu and tibia II of male. Scale bar = 100 µm for 9, 10, 12, 13, 50 µm for 11.