Metoponia robertsoni

Daniels, Greg, 2016, A new genus and two new species of soldier fly (Diptera: Stratiomyidae: Chiromyzinae) from Australia, one found infesting sugarcane in central Queensland, Zootaxa 4092 (2), pp. 572-582 : 575-579

Metridius robertsoni nov. sp.

( Figs 1–21 )

Diagnosis. Metridius robertsoni nov. sp. can be distinguished by having the vertex raised well above the eyes, an apparently unsegmented antennal flagellum (flagellomere 1 sometimes present) and the absence of the discal median cell.

Material examined. HOLOTYPE ♂, AUSTRALIA, Queensland, Carmila, collected sugarcane soil 30.v.1983, emerged 14.vi.1983, L.N. Robertson (QM). PARATYPES: Queensland. 1 ♂, same data as holotype except collected 8.vi.1982, emerged 12.vi.1982 (QM); 26 ♂, 24 ♀, same data as holotype except emerged 7– 29.vi.1983 (AM, BMNH, QDPI, QM). Non-type material examined. Queensland. 1 ♂, same data as holotype except emerged 18.vi.1983 (QM).

Description. Male ( Figs 1–8 ). Length (mm): body, 6.2–6.5; thorax, 1.6–1.7; wing, 6.0–6.3. Head ( Figs 1–2 ). Transversely broadened; ocellar tubercle black, distinctly raised above vertex. Face and frons yellow brown with long, mostly erect, black setae. Frons visible when viewed laterally. Frontal index 0.5–0.7. Ratio of frons width to head width 1.0:2.5–2.6. Face at narrowest about one-third of head width. Eye height less than head height. Antenna ( Fig. 5 ) brown-black and about twice as long as head height. Antennal scape and pedicel setose, flagellum pruinose, flagellomeres poorly defined; relative lengths of antennal segments 1.8–2.4:1.0:9.5–23.8. Palpus black.

Thorax. Mostly deep brown, with scutellum, humeral callus, postalar callus and laterotergite yellowish. Scutum, dorsal anepisternal margin and katepisternum with long fine yellow setae. Legs mostly brownish yellow; hind tibia with yellowish central area; all femora with admixed black and yellow setae; tarsomeres and tibiae with mostly black setae. First tarsomere on all legs as long as or longer than tibia.

Wing. ( Fig. 4 ). Hyaline, membrane entirely with microtrichia; vein R1 setulose dorsally along length, R2+3 and R4+5 dorsally setulose distally. R4+5 unbranched. Discal medial cell absent. Halter long, pale yellow. Alula narrow.

Abdomen. Brownish with pale yellowish setae. Terminalia ( Figs 6–8 ). Small, brownish yellow. Cerci onesegmented. Aedeagus single pronged. Gonocoxite medially attenuate distally, extending almost to apex of aedeagus.

Female ( Figs 9–15 ). As male except as follows. Length (mm): body, 6.4–9.8; thorax, 1.2–1.4. Head ( Figs 9– 10 ). Yellowish; frons at narrowest about two-thirds head width and with short, erect black setae, less dense than in male. Frontal index 0.6–0.7. Ratio of frons width to head width 1.0:1.5–1.7. Eyes with very short, sparse ommatrichia. Antenna slightly longer than head height. Scape, pedicel and flagellum with setae restricted mostly to apex of each; flagellomeres poorly defined; relative lengths of segments 1.4–1.8:1.0:3.9–6.2. Face with long, black, marginal setae, oral tubercle yellow and slightly raised. Vertex with two dorsal calli near ocellar tubercle, extending beyond the upper margin of eyes.

Thorax. Yellow-brown. Mesonotum with short, fine, yellow setae. Lateral thoracic pleura absent, except for meropleurite, propleuron and katepisternum which are well defined. Small pit present near where wing base should be and a larger, deep pit above and anterior to katepisternum. Metathoracic and mesothoracic spiracle present. Halter entirely absent. Legs shorter than male and first tarsomere shorter than tibiae.

Wings. Absent.

Abdomen. Brownish with fine, yellow setae. Tergites and sternites separated from thoracic sclerites by narrow membranous band. On dried specimens sternite 1 appears to be divided medially but this is not evident when abdomen is slide mounted. Terminalia ( Figs 13–15 ). Yellow. Ovipositor is not apparent; sternite 8 viewed ventrally is convex and longer than combined length of tergites 8 and 9. Cerci two-segmented and of equal length, the basal segment broad at base and tapering to basal width of segment 2. Genital furca with short posteromedian projections and a large median aperature.

Larva ( Figs 16–21 ) (based on a larva of similar size to a seventh or eighth instar larva of I. rubriceps ). Length 10.4 mm, maximum width 2.5 mm.

General colour yellow-brown. Entire body surface bearing rounded, slightly raised cuticular plates. Anterior margin of clypeofrons blunt, slightly rounded. Antenna absent. Anterior prothoracic spiracle set dorsad to lateral margin of segment and not protruding over margin of segment and therefore, not visible when viewed ventrally. Sternal patch on sternite 6 long and narrow, on sternite 5 slightly shorter. Anal segment rounded posteriorly. Pupal respiratory horns very short and visible on segments 1–6. Chaetotaxy. All setae on head short and simple. Thoracic and abdominal setae flat with frayed apical margin and arranged in transverse rows. Primary dorsal and primary ventral setae longer than secondary dorsal and secondary ventral setae. Anal segment without marginal fringe of setae and with distinct apical and subapical setae, which are not apically flattened.

Biology and Ecology (adapted from Les Robertson's field notes). On 8 June 1982, 15 puparia of M. robertsoni nov. sp. were collected from soil samples taken under sugarcane. The soil was silty sand from the alluvial terrace of Carmilla Creek at Carmilla, Queensland. Five (1 ♂, 4 ♀) adults emerged between 8–12 June 1982 and all died within 4 days of emergence. The following parasites also emerged: 1 Megastylus sp. ( Hymenoptera : Ichneumonidae ), emerged 8 June 1982; 2 Neurogalesus militis Osborn, Forteath and Holloway ( Hymenoptera : Diapriidae ), emerged 12 and 25 June 1982. The latter is also recorded as a parasite of Inopus rubriceps (Osborn et al., 1973) . Several larvae collected at the same time were infected with the fungus Metarhizium anisopliae var. anisopliae (Metsch.) Sorok.

On 30 May 1983, 170 live puparia, 147 empty puparia and 11 Metarhizium -killed larvae of M. robertsoni nov. sp. were recovered from the same locality in sugarcane, which was showing signs of severe damage, typical of stratiomyid larval feeding (partial to complete ratoon failure and reduced cane growth). The pupal density was estimated to be 2000 per m2 soil surface. Several males were collected by sweep-netting over weeds in the damaged cane patch.

The field collected puparia produced 34 ♂ and 28 ♀ M. robertsoni nov. sp., 19 N. militis and 2 Neurogalesus sp. Thirty four larvae of a total of 42 collected with the puparia pupated to produce 22 ♂ and 12 ♀. The pupal period was 18–21 days at 20+/-2ºC.

Mating occurred in the rearing box soon after emergence and eggs were laid within hours of mating. Viable eggs turned amber within one or two days (see also Gerard (1979) for I. rubriceps egg colour change) and three egg clusters observed took ten days to hatch at 20+/-2ºC.

One egg cluster laid in June 1982 contained 157 eggs. This was laid by an unmated female approximately 24 hours after emergence and may not have been the full complement of eggs. Four fully gravid females when dissected contained 189, 226, 247 and 361 eggs respectively and the ovaries containing the full complement of mature eggs occupied almost all of the thoracic cavity as well as the abdomen.

The pharate adult can be observed through the late stage puparium and can be sexed. Weights of sexed pupae were as follows: ♂, x = 7.93 mg, range = 6.7–9.2, N = 7; ♀, x = 21.22 mg, range = 14.5–30.2, N = 5.

Etymology. The species name honours Les Robertson who collected the specimens and provided biological data.

Geographic distribution. Australia (Queensland).

Comments. The larva of M. robertsoni nov. sp. is very similar to I. rubriceps and I. flavus , of which the position and size of setae are similar but the apically broadened and flattened setae distinguish M. robertsoni nov. sp. from the other two species. Other characters are summarised in Table 2 .

Figures

FIGURES 1 – 8. Metridius robertsoni nov. sp., male paratypes. (1). Head, lateral view. (2). Head, anterior view. (3). Lateral habitus. (4). Wing. (5). Antenna. (6). Genital capsule, dorsal view with epandrium, proctiger and cerci excluded. (7). Genital capsule, ventral view. (8). Epandrium, proctiger and cerci. Abbreviations: aed, aedeagus; ce, cercus; ep, epandrium; gonocx, gonocoxite; gonost, gonostylus; pr, poctiger. Scale bar, 0.25 mm.

FIGURES 9 – 15. Metridius robertsoni nov. sp., female paratypes. (9). Head, lateral view. (10). Head, frontal view. (11). Lateral habitus. (12). Dorsal habitus. (13). Terminalia, dorsal view. (14). Terminalia, lateral view. (15). Terminalia, ventral view. Abbreviations: ce, cercus; st, sternite; tg, tergite. Scale bar, 0.2 mm.

FIGURES 16 – 21. Metridius robertsoni nov. sp., larva. (16). Head and thoracic segment 1, dorsal view. (17). Abdominal segment 3, dorsal view. (18). Anal segment, dorsal view. (19). Head and thoracic segment 1, ventral view. (20). Sternites 5 and 6, ventral view. (21). Anal segment, ventral view. Abbreviations: pdl, primary dorsolateral seta; pvl, primary ventrolateral seta; spa, sternal patch; st, sternite; sdl, secondary dorsolateral seta; svl, secondary ventrolateral seta. Scale bar, 1.0 mm.