Diogma glabrata, (MEIGEN, 1818)

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 : 1177-1179

DIOGMA GLABRATA (MEIGEN, 1818)

( FIGS 3B , 5B , 14A–C )

Life history: The whole life-cycle of this species is completed in one year ( Müggenburg, 1901); in Japan, the adult flying period is in summer (July to August), which is much later than the other co-occurring species ( Liogma mikado and Liogma serraticornis ). Larvae are found in terrestrial mosses growing on stones in limestone woodlands, and also in moss mats growing on soil. In Europe, they were found in forests in grassy, humid areas with Rhytidiadelphus squarrosus (Hedw.) Warnst. ( Hypnales : Hylocomniaceae) ( Zeller, 1842; Müggenburg, 1901). The number of moults is unknown. Final-instar larvae apparently do not have a preference for pupation sites and pupae were found anywhere in the lower damp layers of moss carpets ( Alexander, 1920).

Oviposition: A female of this species laid about 60 eggs in total ( Müggenburg, 1901), depositing them singly on the lower surface of leaves or stems of mosses ( Hemmingsen, 1960).

Egg: Length 1–1.3 mm ( Müggenburg, 1901). Spindleshaped, circular in cross-section, with a slightly tapered front pole; longitudinally bulbous ( Peus, 1952). Chorionic sculpture irregularly jagged, occuring closeset; reticulated near micropyle ( Peus, 1952).

First-instar larva: Newly hatched larvae ashy grey, but become moss green in colour at later stages ( Müggenburg, 1901).

Final-instar larva: Length 17–18 mm (N = 3). Body colour with dark green hue; dark pigmentation appears as small blotches on lateral sides, with various forms ranging from rhombus to trapezoid; also, a single, small, isolated blotch near the distal corner of the anterior end is present in the abdominal segment; size of pigmented area increases from abdominal segments I to VI; pigmentation small and pale on abdominal segment VII ( Fig. 14A, B ). Brown individual unknown (Müggenberg, 1901; Wesenberg-Lund, 1915; Alexander, 1920). Prothorax rugulose; dorsal lobes conical with sharply pointed apices, two pairs along pronotal ridge, anterior pair longer than posterior pair ( Fig. 5B ); lateral lobes one pair; ventral lobes two pairs. Meso- and metathoracic segments have two pairs of dorsal lobes; lateral lobes two pairs; ventral lobes two pairs, papilla-like, anterior pair closer to each other than posterior pair ( Fig. 5B ). Dorsal lobes on abdominal segments with bluntly pointed apices, third and fourth pairs bearing two, rounded auxiliary outgrowths ( Fig. 6B ); segment I with two pairs of lobes, each with two auxiliary outgrowths at the front; segments II–VII with four pairs, each of the posterior two pairs carry two teeth-like auxiliary outgrowths at the front, fourth pair longest and stout; segment VIII with a pair of small, simple, conical lobes without auxiliary outgrowth. Lateral lobes on abdominal segments simple, finger-shaped; segments I and II–VI with three and four pairs, respectively. Ventral lobes on abdominal segments rounded. Anal segment with one pair of dorsal lobes long; dorsomedial lobes (dm) one pair, short and conical ( Fig. 14C ); lateral lobes one pair, papilla-like; ventral lobes two pairs, anterior pair papilla-like. Spiracular field with hair fringe.

Host-plants: Larvae feed on Rhytidiadelphus squarrosus ( Hypnales : Hylocomiaceae ) and Hypnum cupressiforme Hedw. ( Hypnales : Hypnaceae ) ( Zeller, 1842; Müggenburg, 1901). At mixed forest near Mt. Kisokomagatake (Nagano, Japan), at least two larvae have been confirmed to feed on Bryhnia cf. tenerrima ( Hypnales : Brachytheciaceae ) in the field.

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.

Figure 6. Comparative morphology of dorsal elongated cuticular appendages on abdominal segment in cylindrotomine larvae at late instar. (A) Cylindrotoma japonica. (B) Diogma glabrata. (C) Liogma brevipecten. (D) L. mikado. (E) L. nodicornis. (F) L. serraticornis. (G) Triogma kuwanai. (H) Phalacrocera replicata. For C, E and H, body colour is faded away due to preservation in alcohol. Scale = 1 mm.

Figure 14. Biology and morphology of Diogma glabrata. (A) Final instar larva of D. glabrata. (B) Later-instar larva feeding on Bryhnia cf. tenerrima (Brachytheciaceae). (C) Characters of anal segment. Abbreviations: dl, dorsal lobe; dm, dorsomedial lobe; vl, ventral lobe. Scale = 1 mm.