Prosopochrysa vitripennis ( Doleschall, 1856 )

Prosopochrysa vitripennis ( Doleschall, 1856) View in CoL

Chrijsochlora vitripennis Doleschall, 1856: 408 View in CoL .

Microchrysa albitarsis Brunetti, 1913 View in CoL

Description of larva and puparium

Mature larva ( Figs. 1–17). Shape and colour ( Fig. 17). Elongate, slightly dorsoventrally flattened, abdominal segments slightly tapering and elongated towards caudal end. Head mostly yellowish-brown, only dorsomedial and ventral sclerites darkened brown. Lateral sclerites (genae, ocular plates) predominantly yellowish-brown. Oral opening and basal segment of antenna brown. Body segments yellowish brown in ground colour, with brown and yellow pattern. Thoracic segment 1 yellowish brown with six (= three pairs) yellow anteroposteriorly elongated patches forming distinct bands on each side of the darkened middle. All pairs of bands extend to posterior edge of segment; lateral yellow bands extend to lateral edges of segment. Small round or oval dark brown spots arranged in small groups either of 4-6 or irregularly over entire segment area. Thoracic segment 2 with yellow and brown patches and spots forming a distinct pattern. The same pattern is more or less distinct on all other segments except the last abdominal segment. The pattern on the last abdominal (anal) segment is limited to a brown central band and brownish longitudinal narrow stripes on each side. Venter of body segments yellowish-brown in ground colour. All thoracic and abdominal segments with small dark brown spots, sometimes arranged in circular or lateral symmetrical groups.

Head ( Figs. 1–3; 7–11) only slightly retracted into thoracic segment 1, longer than wide in dorsal view, head index (length: width) 1.3–1.4. Labrum slightly longer than anterolateral corners of head capsule. Eyes distinctly convex, in dorsolateral position, same colour as surrounding area. Two-segmented long antennae located at the anterolateral angles of the head capsule (a, in Figs. 10, 11). Basal segment of antenna about twice as long as wide; apical segment more than three times as long as wide, and conical. One long finger-like sensilla, longer than apical segment of antenna, and three short finger-like sensilla visible beside apical segment (se, in Fig. 11).

Mandibular-maxillary complex densely haired, with more or less distinct transverse rows of flat setae, finger-like maxillary palpus relatively long. Ventral opening of head capsule well-developed, covered with fine membrane.

Body segments. Larval body composed of three thoracic and eight abdominal segments. Thoracic segment 1 (prothorax) more than twice as wide as long. Thoracic segments 2 and 3 almost four times as wide as long. Abdominal segments gradually narrowing and elongating towards distal end: segments 1–3 almost three times as wide as long, segment 5 almost three times as wide as long, segment 7 almost 2.5 times as wide as long. Strong ventral hooks developed on posterior margin of abdominal segment 7 (h, in Figs. 5, 15). Anal segment short, almost as long as wide (index of mature larvae about 0.9). Oval anal slit located near base of anal segment occupying almost half of segment length ( Figs. 5, 15). The sclerotised lips of the spiracular opening form spiracular plates. Dorsal spiracular plate narrow, ventral spiracular plate large and deeply emarginated in middle (dp, vp, in Figs. 6, 16). Pointed, conspicuous lateral projection present on anterior corners of thoracic segment 3 and all abdominal segments except last (anal) segment ( Figs. 4, 5). Thoracic segments 2 and 3 adorned with rounded lateral projections near posterior margin of segment; projection on segment 2 larger than on segment 3. Narrow sternal patches present on abdominal segments 6 and 7.

Respiratory system. Anterior spiracle, placed on conical tubes on each side of thoracic segment 1, small, oblique oval ( Fig. 1). Usually small, inconspicuous, rudimentary and non-functional spiracles on abdominal segments 2–5, poorly visible. Transverse spiracular opening at distal end of anal segment surrounded by pinnate float hairs arising from dorsal and ventral spiracular plate ( Figs. 5, 6, 15, 16).

Chaetotaxy. All characteristic setae of head present. Head capsule with conspicuously haired ventral surface ( Figs. 2, 3), some major ventral setae barely visible between long dense hairs. Labral setae (Lb1) short and broadly pinnate, Lb2 two-branched with short hairs ( Figs. 2, 8), clypeofrontal setae (Cf1) two-branched and slender, posterior clypeofrontal setae (Cf2) at level of posterior eye margin with one or two branches ( Figs. 1, 2). Slender dorsolateral seta (DL) posterior to eye-prominence and long lateral seta (L) anterior to eye ( Figs. 1, 2). Three pairs of setae present on ventral side of the head. Seta V1 close to ventral opening, bush-like but often almost invisible between marginal hairs of genal lobes, setae V2 bush-like with numerous pubescent branches, setae V3 with two or exceptionally three branches with long pubescence. Ventrolateral setae arranged in an elongated triangle: VL 1 in middle of genal lobe bush-like, VL2 between lateral seta (L) and antenna pubescent in apical part, VL 3 in front of V3, two exceptionally three branches with long pubescence ( Figs. 2, 3).

Setae on body segments mostly poorly visible, weak and hyaline. Chaetotaxy of thoracic segment 1 is complete: 2 pairs of anterodorsal (Ad) and 3 pairs of dorsal (D) setae, setae Ad1 and Ad2, same shape as setae D1 and D2. Setae D3 very weak and long, poorly visible, shifted anteriorly to the transverse line of Ad setae ( Fig. 1). One dorsolateral (DL) and one ventrolateral seta (VL) on each side, both of equal length, almost half as long as segment ( Figs. 1, 3). Ventral side with long and slender outer ventral setae (V2) and simple, partly flattened and short-haired pubescence ventral setae (V1) inserted more medially and slightly anterad. Sparse, pale, short, finger-like hairs present on anterior dorsal margin of segment. Dense, short hairs well developed along anterior ventral margin of segment, occupying slightly more than medial third. Setae D1 and D2 on thoracic segments 2 and 3 in same position, dorsal setae D3 shifted posteriorly to the same transverse line as D1 and D2. Anterodorsal setae absent.

Configuration of dorsal setae on abdominal segments 1–7 very similar to thoracic segments 2 and 3; dorsal D1 and D2 setae pubescent, inserted on same transverse line on abdominal segments 1–3, D2 setae shifted slightly anteriorly on abdominal segments 4–7; D3 setae poorly visible ( Fig. 4). Dorsolateral and ventrolateral setae mostly distinct, on each side of abdominal segments, but only fine and short. Ventral side with three pairs of setae, V1 and V3 setae distinctly flattened and pubescent, simple V2 shifted slightly posteriorly, closer to V1 than to V3 ( Figs. 5, 13, 14).

On dorsal side of anal segment (= abdominal segment 8) one pair of relatively short setae on distal third and two pairs of lateral setae: L1 above middle of segment relatively long; L2 at each posterolateral corner distinct, longer than half of segment length ( Figs. 4, 5). Ventral side with 5 pairs of simple and slender ventral setae being more or less distinct between thick and long hairs (V1 at sides of anal slit, V2 more lateral, V3 at sides of anal slit, approximately in the middle of its length, V4 at level of distal end of anal slit between anal slit and lateral margin of segment and V5 at same level but more medial). Pair of very long apical setae (Ap) distinct on ventral side just above apical coronet. Subapical setae (Sa) present ( Figs. 5, 15).

Measurements. Length: 8.3–10.1 mm; maximum width: 2.0–2.3 mm. Seven larvae examined.

Puparium. The puparium has the same characteristics as the mature larva, with the same length and maximum width. Respiratory horns are present on prothorax (rh, in Figs. 9, 12). Habitat and biology. The larvae of Prosopochrysa vitripennis were found in northern Thailand during the dry season in April and May. They lived in puddles in dry streambeds or on the banks of streams and rivers that had been cut off from the main stream by the falling water levels ( Figs. 18, 19). The puddles were filled with fallen leaves from trees and bamboo. The larvae crawled in the water between the leaves, presumably scraping food particles from the leaf surface. They used a coronet of hydrofuge hairs on the last abdominal segment to breathe at the surface of the water ( Fig. 17). Mature larvae crawled ashore and attached themselves with their posterior ends to the lower, hidden surfaces of fallen leaves protruding from the water. A secretion produced in the anal region was used for fixation. After hardening, the secretion became white and later yellow. The larvae shared their habitat with larvae of the water beetle family Scirtidae , which also use a secretion to attach themselves to leaves before pupation ( Kovac & Klausnitzer, 2020).