Giluwea flavomacula Vockeroth
Very small slender species with male broadly dichoptic, face produced strongly forward below, scutellum black and abdomen black or with small lateral yellow triangles. Face, thorax, and abdomen with well-defined yellow markings (Vockeroth 1969).
Adapted from original description (Vockeroth 1969).
MALE.
Head shining black, submetallic; face with a rather irregular, subtriangular, bright yellow macula on either side against the eye; ventral part of occiput and posterior part of gena grey pollinose. Antenna with first two segments yellow-brown, basoflagelloemre black. Head pile mostly black, only those on pollinose areas white; pile of front rather sparse, moderately long, increasing in length to vertex.
Thorax: Scutum mostly black, shining, with slight metallic reflection laterally behind suture, faintly pollinose only on anterior third, on postcallus, and immediately before scutellum; postpronotum and broad sharply defined presutural scutal margin bright yellow. Scutellum black, shining. Pleura black, very faintly pollinose, with large sharply defined yellow macula below wing covering posterodorsal part of anepisternum, anepimeron except posteroventral corner, and most of anatergum. Pile of scutum and scutellum black, rather sparse, distinctly longer on posterior than, on anterior half of scutum, those of yellow presutural margin and of scutellar margin particularly long and sparse. Pile of pleura long, sparse, mostly white, those of yellow part of anepisternum, and usually also of anepimeron black. Wing clear except for light brown stigma. Calypter white to brownish-white with margin slightly darker; fringe of dorsal calypter partly black, calypter fringe otherwise white. Haltere bright yellow. Legs mostly yellow, dark brown to black as follows: anterior surface of procoxa and all of meso- and metacoxae, extreme base of profemur, about basal 1/4 of mesofemur and basal half of metafemur, apical half -or slightly more of metatibia, and all tarsi. Pile of legs mostly black, those of coxae, trochanters, and lower surfaces of femora mostly white.
Abdomen with terga mostly black, shining. Tergum 1 with anterior corners yellow; terga 2 to 4 each with a pair of small yellow lateral triangles which extend broadly to lateral margin, those of tergum 2 extended narrowly forward laterally almost to base of tergum. Sterna 1 to 4 black, mostly shining; sterna of postabdomen pollinose, variously yellow, brown, or blackish. Genitalia: left surstylus with ventral margin nearly straight, the posteroventral angle only very slightly produced. Right surstylus tremendously enlarged and inflated, strongly convex externally and concave internally, in retracted position partly covering the left surstylus like a hood, with long sparse setulae dorsally and on part of inner surface, otherwise almost bare. Sternite 9 with many very short fine hairs on lateral surface of posterolateral process. Left superior lobe with posterior surface slightly broadened and concave, the posterolateral margin compressed, the posteromedian margin minutely serrate on middle 1/3, the dorsal portion greatly broadened and curved moderately anterolaterad to end in a subacute point with two notches on anterior margin below this point; lateral surface of lobe with a few minute setae. Right superior lobe not broadened posteriorly, the posterior margin moderately compressed on dorsal 2/3, the anterior portion considerably broadened from base to 2/3 its length where it curves laterad as a tapering subacute process, tapering on apical 1/3 to a bluntly rounded apex; lateral surface with a few minute setae. Distal portion of aedeagus with minute pale setulae at apex.
FEMALE.
Very similar to male. Front and abdomen broader. Yellow markings of abdomen often reddish and usually much reduced so that tergum 2 has a lateral pale vitta only slightly broadened at 2/3 the length of the segment, tergum 3 has a small lateral pale spot, and tergum 4 is only very obscurely paler on lateral margin.
Body length 5.2 to 5.9 mm (Vockeroth 1969).
This very peculiar genus appears to have no close relatives. Only three other groups have dichoptic males but there is no indication of any relationship among the four. One of these, Melangyna (Melanosyrphus), also occurs at high altitudes in New Guinea, and like Giluwea has the face produced below, but it has symmetrical genitalia and lacks the swelling at the base of the costa found in both species of Giluwea. A second group, Eosphaerophoria, is widespread in the Oriental region; it too lacks the costal swelling, has the scutellum acute or subacute apically, has aberrant wing venation, and has the male genitalia with sternite 9, the superior lobes and the aedeagus strongly asymmetrical but the surstyli symmetrical. The third group, a single species of Allograpta from New Zealand, is undoubtedly not related to Giluwea. It is tempting to speculate that the species of Giluwea may have dichoptic males because of their occurrence in high open montane areas and a subsequent change in flight and mating habits. However, the other groups with dichoptic males occur at lower altitudes, so this attempted explanation would not apply to them (from Vockeroth 1969).
Species only known from Mt. Giluwe, Papua New Guinea.