Dasybasis exulans (Erichson, 1842)

Ferguson, David J. & Yeates, David K., 2015, A new species, new immature stages, and new synonymy in Australian Dasybasis flies (Diptera: Tabanidae: Diachlorini), Zootaxa 3946 (2), pp. 261-273 : 269-272

Dasybasis exulans (Erichson, 1842)

Figure 11 , 12

Larva. Length: 23–26 mm long and 3.5–4 mm wide ( Fig. 11 A). Thoracic segments 1–3 tapering anteriorly; with the 1st segment near half the length of the 2nd segment; abdominal segment I similar to thoracic segment 3; abdominal segment II–IV are of similar diameter, lengthening posteriorly; segments V–VII tapered posteriorly; all segments with fine longitudinal surface striations; colour creamy white with grey-brown bands anterodorsally. Head capsule ( Figs. 11 C, D) retractable, measuring 5.5 mm long from the tip of the labrum to the posterior bilobed extremity of the epicranium; greatest width 1 mm; anterior darkly sclerotised; cranium (cr) weakly sclerotised; labrum laterally compressed with patches of short spines on lower lateral surfaces; distal mandibular hook heavily sclerotised, black, curved with serrated lower edge; mandibular brush bristles pale; anterior margin of the maxilla broad, tapering to an acute apex ( Fig. 11 C); maxillary lacinia broad at the base, terminating in a short narrow posteriorly directed apex, inner surface with short pale spines; maxillary palp short with 2 segments; antenna arises from the anterolateral subapical surface of a forward projecting process; 1st segment tapered to a narrow, concave apex, holding two very small and thin microsetae that appear connected at their base; labium ( Fig. 11 B) anterior edge with 3 small projections, medially with deep cleft; tentorial rods dorsally troughed medially, divided subapically. Thorax. ( Fig. 11 A), prothorax annulus with 5 posteriorly directed areas of pale brown granular membrane, these tapered areas extending ¾ the length of the segment I; segment II–III with broad collar of anterodorsal granular membrane. Abdomen. ( Fig. 11 A), anterodorsal bands on abdominal segments II–V are greybrown and become narrow laterally. Segments I–V with 3 pairs of prolegs on each side, segments VI–VII with a pair of smaller prolegs on ventral surface; apex of all prolegs with granular membrane; segments VII with lateralline of pores on posterior half of segment; segment VIII, posterior spiracle ( Fig. 11 E) with a relatively simple relatively smooth sclerotised surface medially, with textured surfaces on the dorsal and ventral surfaces; margin undulate with deep cleft extending medially; many evenly spaced branched filaments distributed along the distal margins.

Pupa. Length: 18 mm ( Fig.12 A). Head: The cephalothoracic setae arise from a conical basal tubercle ( Fig. 12 B); setae long, apical third laterally compressed and curled; callus setae and vertical setae long and slender; callus tubercle apically tapered; antennal ridge sub triangular in cross-section, darkly sclerotised and anteroventrally directed; antennal sheath tapered with apical tooth; abdominal orbital seta and posterior orbital seta long and slender, tubercles apically tapered; lateral orbital seta long and slender, tubercles joined. Thorax. Anterolateral spiracle ( Fig. 12 C) bulging; basal alar seta long and slender; anterior mesonotal seta and posterior mesonotal seta long and slender. Abdomen. Pleural setae long and slender, basal tubercles conical, evenly spaced; abdominal segment 2–7 with abdominal spiracle anteriomedially placed on each pleura; each segment with a spinous fringe of pale spines on the posterior margin that are generally curved inward; segment 8 with 3 combs of setae: dorsal comb with 9 robust setae; lateral comb with 8 slightly weaker setae; ventral comb with 7–8 robust setae. Aster ( Fig. 12 D), posterior surface swollen, with deep dorsoventral suture medially; dorsal, lateral and ventral tubercles of the aster broad, edges serrated, longitudinally compressed with lateral edges darkly sclerotized.

Remarks. Larvae and pupae were collected from the rich ecological niche of under seaweed wracks that support a mix of crustaceans, spiders, terrestrial earth worms, both larvae and adult Sphargeris physodes Pascos ( Tenebrionidae : Lagriinae : Caerodini), and larvae belonging to Therevidae (Diptera) .

Larval and adult D. exulans appeared to dominate the beach, with only a few adult D. reiki collected. This was also observed in the twenty-two pupae exuviae collected after gale force winds eroded the beach surface, where 20 where identified as D. exulans and two D. reiki .

The coloration of both sexes of D. rieki is very similar. Females of D. rieki can be readily separated from D. exulans by a number of features; Dasybasis rieki frontal callus is near square in shape, ( D. exulans frontal callus is rectangular), the pleuron and coxal hairs are silver-white, and the abdominal sternites are densely covered in grey pubescence that obscures the integument colour, (in D. exulans , the pleuron and coxal hairs are sparse and greywhite or pale yellowish; the sternites are thinly covered in grey pubescence allowing the integumental colour to be seen underneath).

The larva of D. rieki are a cream-white in colour, and without distinctive dorsal banding as found in D. exulans ( Figs 11 vs 9). The tubercles of the aster of the pupae are very distinctive and diagnostic. Dasybasis rieki are conical, compact and curved posteriorly appearing ‘claw like’, D. exulans broadly flattened, and laterally directed.

Figures

FIGURE 11. Dasybasis exulans. A, larva, length 23 mm; B, (lm.) labium, width 0.15 mm; C, larval head lateral view, length 5.5 mm; D, larval head dorsal view; E, posterior spiracle structure, dorsoventral length 1.8 mm.

FIGURE 12. Dasybasis exulans. A, pupa, length 21 mm; B, basal tubercle of setae, basal width 0.2 mm; C, anterolateral spiracle structure, length 1.8 mm; D, aster, width 2 mm.