Triogma kuwanai, (ALEXANDER, 1913)

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 : 1184-1186

TRIOGMA KUWANAI (ALEXANDER, 1913)

( FIGS 1A , 2C , 5H , 6G , 17A–F )

Notes: Triogma kuwanai used to be subdivided into two subspecies, T. kuwanai kuwanai (Honshu) and T. kuwanai limbinervis (Shikoku) , but T. limbinervis Alexander, 1953 can be treated as a species ( Oosterbroek 2020). The accounts below are based on T. kuwanai kuwanai .

Life history: In Japan, adults often fly together with species of L. mikado , L. serraticornis and L. brevipecten at the same locality and about the same period of time (May–June, in Honshu). Larvae are found in moss patches on the forest floor. The cuticular surface is heavily armoured with debris and epibionts, which seems to be related to the cryptic habitat.

Adult behaviour: Three adults were observed on 18 May 2016, Ikawa-touge, Shizuoka, Japan. They occasionally flew over the shaded forest floor when disturbed, but soon returned to the original position. Adult males generally perched on a moss mat, whereas females usually rested hanging on branches or near the damp soil. Eggs were laid on the leaves of the following plant species: Pohlia longicolla (Hedw.) Lindb. (Bryaceae) (four eggs), Mnium heterophyllum (Hook.) Schwaegr. (Mniaceae) (two eggs), Plagiothecium curvifolicum Limpricht (Plagiotheciaceae) (one egg), young shoots of Stellaria media (two eggs) and a sprout of an unidentified species of fern (one egg). Two eggs were laid on the shallow layer of soil. Larvae hatched 10–11 days later from 20 out of 29 eggs. Three larvae perforated and fed on the leaves of M. heterophyllum . All reared larvae died before reaching the second instar.

Egg: Length 1.3 mm (N = 1). Spindle-shaped, circular in cross-section, with a tapered front pole. Pale grey due to exochorionic sculpture, with yellowish tint of egg content ( Fig. 2C ), yet apparently lighter than L. brevipecten . Chorionic sculpture elongated and narrow, arranged as irregularly jagged, dotted dash lines; reticulated near micropyle.

First-instar larva: Length 2.9 mm (N = 4). Hyaline ( Fig. 17D ). Dorsal elongated cuticular lobes on thoracic and abdominal segments acutely bent backwards (or occasionally forward).

Final-instar larva: Body with dark brown hue ( Fig. 17A ). Integument entirely rugulose with velvet-like texture, retaining high opacity in alcohol; dark pigmentation diffused on dorsal side, densest near dorsal lobes, making stripes in parallel with longitudinal body axis; small patch with purple lustre at bases of dorsal lobes ( Fig. 17E ). Prothorax dorsally with six tubercles along pronotal ridge; one pair of lateral lobes; ventral lobe absent. Meso- and metathorax with two pairs of dorsal lobes, posterior pair bearing two auxiliary outgrowths at the front; two pairs of lateral lobes, anterior pair longer; two pairs of ventral lobes, anterior pair more widely separated from each other than the posterior pair. Dorsal lobes on abdominal segments slender and apices acutely bent backwards ( Fig. 6G ); four pairs on abdominal segments I–VII, two anterior pairs smallest, and fourth pair longest with three auxiliary outgrowths at front. Lateral lobes relatively long and broad, apices strongly bent backwards. Ventral lobes on abdominal segments relatively long and finger-like ( Fig. 17E ). Anal segment ( Fig. 17C ) with one pair of dorsal lobes; dorsomedial lobes absent; two pairs of ventral lobes, anterior pair papilla-like. Spiracular field with hair fringe.

Host-plants: Although larvae are found amid moss tufts of Mniaceae (Bryales) , together with Liogma serraticornis , this species probably does not feed on them. One late-instar larva was found feeding on Brachythecium brotheri Paris ( Hypnales : Brachytheciaceae ). Under rearing conditions, first instar does not survive on the host-plants used for female oviposition (as noted above), including three moss species, Pohlia longicolla (Hedw.) Lindb. (N = 4), Mnium heterophyllum (Hook.) Schwaegr. ( Bryales : Mniaceae ) (N = 2), Plagiothecium curvifolicum Limpricht ( Hypnales : Plagiotheciaceae ) (N = 1), although they chew on some leaves of these plants.

Figures

Figure 1. Life history of Cylindrotominae. (A) First-instar larva of Triogma kuwanai consuming fluid within a leaf of Plagiomnium vesicatum (Mniaceae), dorsal view; cells devoid of chlorophyll (black arrowheads) indicate the piercing-andsucking feeding method. (B) Final-instar larva of Liogma brevipecten chewing a leaf margin of Rhizomnium tuomikoskii (Mniaceae), lateral view; note that the head capsule is fully retracted within the lip-like cuticular lobe. (C) Pupa of Liogma brevipecten with a green hue and displaying transverse black stripes in abdominal segments, dorsal view. (D) Copulating couple of Liogma mikado on moss tufts; the female, on the left, was dragged out of the pupal exuvium by the male and thus the body has not been completely sclerotised. (E) Leaf of Stellaria (Caryophyllaceae) with two characteristic incisions in the epidermis of the lower leaf surface (white arrowheads) due to endophytic oviposition; the eggs are absent. (F) Egg of L. mikado laid on a shoot of Hylocomnium splendens (Hylocomniaceae). (G) Larva of C. japonica, which is being preyed upon by what is presumably a third-instar nymph of Himacerus apterus (Hemiptera: Nabidae). Scale = 1 mm.

Figure 2. Eggs of Cylindrotominae (Cylindrotomidae). (A) Liogma brevipecten, dorsal (left) and ventral sides (right); micropyle at the distal end (black arrowhead) and possess a lateral adhesive region (white arrowhead). (B) Liogma brevipecten on the lower side of a liverwort thallus of Conocephalum conicum (Conocephalaceae). (C) Triogma kuwanai, on a dicot shoot. Scale = 500 µm.

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 17. Larvae of Triogma kuwanai. (A) Specimen of late-instar larva preserved in alcohol, dorsal view. (B) Characters of head. (C) Characters of anal segment. (D) First-instar larva. (E) Late-instar larva, ventral view. (F) Adult female ovipositing a single egg on a young shoot of Pohlia longicolla (Bryales: Bryaceae). Abbreviations: dl, dorsal lobe; pr, pronotal ridge; vl, ventral lobe. Scale = 1 mm.