Strobliella intermedia Kieffer

Jaschhof, Mathias, 2017, Catochini, Strobliellini and Acoenoniini revisited: a taxonomic review of the small tribes of the Micromyinae (Diptera: Cecidomyiidae), Zootaxa 4250 (3), pp. 275-295 : 288-290

Strobliella intermedia Kieffer

Fig. 8A–E

Edwards (1938) noted that both sexes of Strobliella intermedia had similar antennae, which is something I doubt, because all other Micromyinae have sexually dimorphic flagellomeres. Edwards’s (1938: fig. 7c) illustration of a flagellomere of the type male shows an ovoid node without crenulate whorl but, in Edwards’s words, with “a sparse median whorl of long spreading dark hairs”. This is the condition found in female Groveriella baltica (see above) as well as in two female Strobliellini from the United Kingdom that Edwards (1938) regarded as belonging to Strobliella intermedia (see Jaschhof 1998: fig. 41a). The only explanation I have for this situation is that the specimen depicted by Edwards was an intersex, with female antennae and male genitalia. In my experience, intersexual individuals of Micromyinae are common enough as to take such a possibility into consideration. The only other male previously thought to be S. intermedia is from Alaska (see Jaschhof 1998: fig. 41c–d), but my study of the three European males reported here makes me wonder whether the Alaskan male could be a different species (see the differential diagnosis below). The antennae of the Nearctic specimen are incomplete and collapsed, so are useless for assessing the exact structure of the flagellomeres (see Jaschhof 1998: 126). Whether the two British females described by both Edwards (1938) and Jaschhof (1998) belong to S. intermedia or a different species remains an unsolved question. Here I redescribe the male morphology of S. intermedia on the basis of three specimens from Sweden and the Slovak Republic, confident that my identification is correct.

Diagnosis. Male Strobliella intermedia are typical Strobliellini , with 21–22 flagellomeres, a single-branched M1+2, and M4 waning basally. Specific to this species, the generally subtrapezoid tegmen has distinct shoulders subapically, with the portion distad of the shoulders weakly sclerotized and bilobed, despite the apparently not absolutely stable outline ( Edwards 1938: fig. 7d; this paper, Fig. 8A ). The stout gonostyli are provided with an apical tooth consisting of several coarse spines that are fused together basally; the tooth appears two- to fourpointed apically, depending on the viewing angle ( Fig. 8A–C ).

Differential diagnosis. Jaschhof (1998: fig. 41c–d) depicted the genitalic structures of a Strobliella male from Alaska, which might be a species different from S. intermedia . The gonostyli of that specimen are more slender apically (fig. 41c) and the tegmen lacks distinct shoulders (fig. 41d). As the outline of gonostyli ( Fig. 8A–C ) and tegmen varies slightly in S. intermedia from Europe, the differences noticed in the Nearctic male need to be substantiated with more specimens.

Other male characters. Body size 2.5 mm. Head. Postfrons asetose. Eye-bridge 4–5 ommatidia long, shortest at vertex. No distinct postocular bristles. Antenna: scape larger than pedicel, both setose ventrally; flagellomeres with short, thick, barrel-shaped nodes; neck and node of fourth flagellomere equally long, node with 1 whorl of short setae basally, 1 complete and 2 incomplete crenulate whorls medially / distally, several hair-shaped translucent sensilla distally ( Fig. 8D ). Palpus length two thirds the head height, 4 segments, first segment with translucent sensilla, apical segment longest (see Edwards 1938: fig. 7b). Thorax. Antepronotum with 0–1 seta. Scutum with lateral and dorsocentral rows of setae. Scutellum with scattered setae of various sizes. Wing (see Edwards 1938: fig. 7a) longer than body. Membrane smoky-brownish, densely setose. Rs oblique, 1.5 times the length of r-m. M1+2 vanishing apically. Legs densely covered with setae of various sizes. Claws strong, bent, with about 5 teeth (described by Edwards (1938) as simple); empodia rudimentary ( Fig. 8E ). Abdomen. All segments approximately same size. First sternite asetose, all other sclerites with setae of various sizes, setae denser laterally than elsewhere. Terminalia ( Fig. 8A ). Ninth tergite trapezoid. Gonocoxites about as long as wide, membranous rather than sclerotized ventrobasally; ventral emargination deep V-shaped; dorsal apodemes thick, long, ending at same level as ventrobasal gonocoxal margin, the latter slightly concave. Gonostylus 1.6 times longer than wide, evenly slightly tapered from midlength towards apex, outline somewhat variable, with some gonostyli more convex than others ( Fig. 8A–C ). Ejaculatory apodeme longer than tegmen, slightly broadened basally, a membranous, microtrichose cap apically; ducts of accessory glands (not depicted) membranous, well discernible. Cerci (not depicted) large, ovoid, setose. Hypoproct (not depicted) much smaller than cerci, with large microtrichia, apparently no setae.

Material studied. New to Sweden: 1 male (CEC404), Småland, Nybro, Bäckebo, Grytsjön NR, haymeadow at forest edge, 18 May–15 June 2006, MT, SMTP (trap 1001, collecting event 1728) (in NHRS) ; 1 male (CEC405), Uppland, Knivsta, Rickebasta, swampy alder forest, 28 May–11 June 2005, MT, SMTP (trap 9, collecting event 1608) (in SDEI). New to Slovak Republic: 1 male, Muránska Planina NP, Muránska Lehota, alder forest, 12 April–24 May 2012, MT, J. Roháček & J. Ševčik (in NMPC) .

Distribution and phenology. Sweden (Småland, Uppland), Austria, Slovak Republic, possibly United Kingdom. Specimens in continental Europe, all males, were collected from mid-April to mid-June in swampy habitats, including alder forest, as far as is known. Two females, possibly this species, from the United Kingdom were collected in September–October ( Edwards 1938).

Figures

FIGURE 8 A – E. Strobliella intermedia, males. A: Genitalia, ventral (specimen from Slovak Republic). B: Gonostylus, ventral (specimen from Sweden). C: Gonostylus, ventral (specimen from Sweden). D: Fourth flagellomere, lateral (specimen from Slovak Republic). E: Acropod of foreleg, lateral (specimen from Slovak Republic). Scales for A – D, 0.05 mm, for E, 0.025 mm.