Triogma trisulcata, (SCHUMMEL, 1829)

Imada, Yume, 2021, Moss mimesis par excellence: integrating previous and new data on the life history and larval ecomorphology of long-bodied craneflies (Diptera: Cylindrotomidae: Cylindrotominae), Zoological Journal of the Linnean Society 193, pp. 1156-1204 : 1186

TRIOGMA TRISULCATA (SCHUMMEL, 1829)

( FIGS 3C , 5I )

Life history: Larvae of this species occur in semiaquatic mosses on moorlands, such as those of Hypnum cuspidatum ( Brindle, 1967) , in stagnant waters on bogs ( Brinkmann, 1997). They have also been found in slowly running water and springs ( Steinmann, 1907 – 08; Hemmingsen, 1968), and in small alpine streams ( Steinmann, 1907 –08; Müller, 1908; Alexander, 1915). According to Haake (1922), the larvae underwent moulting four times until pupation ( Haake, 1922); however, his explanation had a contradictory statement. As Haake (1922) noted, stages I, II and III have one, two and no moulting, respectively, which does not make the total of four instars that the author recorded. First-instar larvae were whitish without distinct colour ( Haake, 1922). The larva lives among the stems of the aquatic moss Fontinalis antipyretica , to which it clings firmly with two strong chitinised hooks at the caudal end of the body ( Haake, 1922). On pupating, it comes to the water surface and remains immobile for the first few days of pupation; after 8–10 days, it becomes more mobile ( Haake, 1922).

Egg: Spindle-shaped, circular in cross-section, with a tapered front pole. Pale yellow. Chorionic sculpture elongated and narrow, arranged as irregularly jagged, dotted dash lines; reticulated near micropyle.

Final-instar larva: Length 19 mm ( Alexander, 1920). Body colour light green with dark blotches ( Alexander, 1920). Prothorax with three pairs of dorsal lobes along pronotal ridge; one pair of lateral lobes; three pairs of ventral lobes as tubercles ( Peus, 1952). Meso- and metathoracic segments with each two pairs of dorsal and lateral lobes; lateral and ventral lobes two and three pairs, respectively ( Alexander, 1920). Dorsal elongated lobes on abdominal segments shorter than body width in ventrolateral view, c. 1.5 mm in length ( Alexander, 1920): abdominal segments II–VII with four pairs of lobes, posteriormost pair longest, bearing three or four teeth-like auxiliary outgrowths at the front ( Alexander, 1915, 1920). Lateral lobes on abdominal segments conical; on segments I and II–VII, three and four pairs, respectively, anteriormost pair smallest ( Alexander, 1920). Ventral lobes small, finger-shapd ( Alexander, 1920). Anal segment with one pair each of dorsal, lateral and ventral lobes. Spiracular field with hair fringe ( Alexander, 1920).

Host-plants: Larvae are found on the submerged moss Fontinalis antipyretica ( Hypnales : Fontinalaceae ), and may also use Hypnum ( Hypnales : Hypnaceae ) and Amblystegium ( Hypnales : Amblystegiaceae ) as hosts ( Wesenberg-Lund, 1943). Brinkmann (1991) reported that one adult emerged from Mnium hornum Hedw. ( Bryales : Mniaceae ).

Figures

Figure 3. Larvae of Cylindrotominae, showing diverse sizes and forms of elongated cuticular appendages. (A) Cylindrotoma distinctissima, ventral (left), lateral (middle), and dorsal (right) views. (B) Diogma glabrata, oblique ventral (left) and lateral (right) views. (C) Triogma trisulcata, oblique ventral (left) and dorsal (right) views. (D) L. mikado, lateral (left) and dorsal (right) view. (E) Phalacrocera tipulina, dorsal view. A–C are redrawn from Peus (1952).

Figure 5. Schematic diagram illustrating diverse arrangements and numbers of the elongated cuticular lobes in 11 cylindrotomine species. Each diagram represents a simplified larval body, longitudinally grouped into six, based on the patterned arrangements of the lobes: (1) prothorax, (2) meso- and metathorax, (3) abdominal segment I, (4) abdominal segment II, (5) abdominal segments III–VII, and (6) abdominal segment VIII (anal segment). Each square partitioned by double lines in a row denotes the integument on the dorsal (dl), lateral (la), ventral (vl) sides of the corresponding segment(s). Each black dot symbolizes a cuticular lobe, of which position/size in a given space express the relative position/size of the lobe.Anal papillae are not shown. Lobe forms, auxiliary outgrowths, and relative length of segments are not shown here (see each species' own description). Each taxon name is abbreviated. For G and I, diagrams are based on the description in Brodo (1967) and Peus (1952), respectively; caution is needed when these are compared with the species examined herein (A–F, I–K), because the lobe characteristics could be treated differently in the previous studies. For K, a single lobe is present at the location of asterisk (*) only in the abdominal segment VII but not in the other segments.