Drusus dudor

Vitecek, Simon, Martini, Jan, Zittra, Carina, Kuhlmann, Hendrik, Vieira, Ariane & Waringer, Johann, 2020, The larva of Drusus dudor Olah, 2017, including an updated key to larval Drusinae Banks, 1916 (Insecta, Trichoptera, Limnephilidae), ZooKeys 908, pp. 137-155 : 137

Description of the 5 th instar larva of Drusus dudor

Biometry.

Body length 10.3-13.8 mm, head width 1.40-1.60 mm (N = 6).

Head.

Head capsule coarsely granulated, outline circular, hypognathous (Figs 1 , 3 ), dorsally chestnut to black brown, with blackish muscle attachment spots. Ventral parietal sections, ventral apotome, maxillolabial sclerites, and premandibular areas yellowish (Figs 2 , 3 ). Eyes surrounded by whitish ring (Fig. 3 ). In lateral view, head capsule with longitudinal carina extending from anterior border of whitish eye ring to anterior parietal border (Fig. 3c ) with antennae located dorsally on central section of carina (Fig. 3a ). Antenna consisting of 1 short cylindrical base and 1 prominent lateral seta. Frontoclypeal apotome bell-shaped, with narrow median constriction (Fig. 1 ). Head capsule with complete set of 18 pairs of primary setae (sensu Wiggins 1998), without additional spines or spinule areas as known from Drusinae grazer clade Groups A and B (Key 1 of the present paper). Primary set of parietal setae consisting of 10 dorsal and 2 ventral primary setae (some of them numbered in Figs 1-3 ), frontoclypeal apotome bearing 6 pairs of primary setae, 3 of them along anterior border. Labrum yellowish brown, anterolateral margins with setal brush and primary setae 1-3; dorsally, setation consisting of primary setae 4-6 (not visible in Fig. 1 ). Ventral apotome cuneiform, medium brown anteriorly, yellowish brown posteriorly, with dark brown anterior transverse suture, postgenal suture reaching approximately 35% of apotome length (Fig. 2 ). Mandibles black brown (sometimes brownish on distal half; Fig. 3 ), spoon-shaped, lacking terminal teeth along edges as well as ridges in central concavity (Fig. 3 ).

Thorax.

Pronotum chestnut brown, very coarsely granulated (Figs 3 - 5 ), posterior margin thickened, fitted with black stripes; no pronotal transverse groove at end of anterior third (Fig. 3 ). In lateral view, with distinct transverse ridge in its posterior third (Figs 3 , 4 ) extending laterally, thereby decreasing in height until ridge is completely faded within lateral center of pronotum (Fig. 3 , dr). In anterior view, ridge with smooth outline (Fig. 5 , smo) and with shallow, V-shaped central notch (Fig. 5 ). Along anterior pronotal border 2 setal rows present, including: i) dense fringe of short, curved, fine, yellow setae, ii) row of widely-spaced long, straight, dark setae not reaching pronotal midline (Fig. 5 , arrows) [in 1 out of 6 larvae, long, straight, dark setae also present near pronotal midline]. Each pronotal half bearing in total 55-63 dark setae of varying lengths in addition to tiny, pale, curved, recumbent setae in low numbers; without spines present in other Drusinae (e.g., D. trifidus ). Prosternite inconspicuous, pentangular, pale yellow, with brown posterior border (Fig. 6 , ps); prosternal horn present (Fig. 6 , ph). Mesonotal sclerites yellowish brown, with dark brown muscle attachment spots and black lateral and posterior borders (Fig. 4 ). Counts for mesonotal setae in anterior setal group sa1: 8-11, in posterior group sa2: 17-20 and in lateral group sa3: 35-46 (Fig. 4 ). In addition, small number of tiny, pale, curved, recumbent setae present. Anterior metanotal sclerites (sclerites of sa1, sensu Wiggins 1998) dark brown, large, broadly triangular, their median separation smaller than their length along the longitudinal body axis (Fig. 4 , sa1); with 7-21 setae. Posteromedian sclerites (sclerites of sa2) dark brown, triangular, with 12-15 setae per sclerite; with 10-12 setae between them (Fig. 4 , sa2). Lateral sclerites (sclerites of sa3) medium to yellowish brown, with 33-37 setae concentrated in cranial section (Fig. 4 , sa3). Groups of 7-9 setae present between sa2 and sa3 (Fig. 4 ). Legs yellowish brown with numerous setae on coxae, trochanters, and femora; tibiae and tarsi sparsely setose (Figs 7-9 ). Foreleg coxa, femur, and tibia wider than those of mid- and hind legs (Fig. 8 ). Femora with several proximodorsal setae (e.g., Fig. 8 , black arrows), and with additional setae on anterior and posterior faces. Fore femora with 4 pale ventral-edge setae, mid and hind femora each with 4 dark ventral-edge setae. Fore trochanters with distal ventral trochanteral brush. Mid- and hind tibiae with dorsal setae only on distal third (Figs 8 , 9 ). Tarsal claws sickle-shaped, pointed, with basal spur (Figs 7-9 ).

Abdomen.

Abdomen cream colored ventrally and laterally, light purple dorsally, with chloride epithelia on abdominal segments II-VII. Abdominal segment I with 1 dorsal and 2 lateral fleshy protuberances (Fig. 4 , lp, dp). Continuous transverse row of setae (some with small basal sclerites) present anterior of dorsal protuberance, comprising fused sa1, sa2, sa3 (Fig. 4 ), meeting dorsal sections of lateral protuberances. No setae posterior of dorsal protuberance (Fig. 4 ). Lateral protuberance without posterior sclerite; anterior of each lateral protuberance, a continuous band of anterolateral setae connects to dorsal and ventral sa3 setal groups (Fig. 10 , bracket). Abdominal sternum I with basal sclerites of central sa2 setae fused, thereby creating multilobed pattern (Fig. 11 ). In total, 91-105 setae present on abdominal sterum I (Fig. 11 ). Abdominal segments II-VIII with 2 dorsal setae (Fig. 12 , ds); only 1 posterolateral seta present on each half of abdominal dorsum IX (Fig. 12 , pls). Abdominal dorsum IX with dark brown, semicircular sclerite bearing 8 long and several short setae (Fig. 13 ). Brown to yellow anal prolegs of limnephilid type (Fig. 12 ), lateral sclerite with 10 dark dorsal and row of 5 dark ventral setae, 3 of the latter very strong and prominent; ventral sole plate with black dorsal stripe and single anterior seta. Anal claw orange, with 1 small dorsal accessory hook (Fig. 14 ). All gills as single filaments. Dorsal gills present at most from abdominal segments II (presegmental) to VI (postsegmental positions). Ventral gills present from segments II (presegmental) to VII (postsegmental). In lateral row, gills present on segments II-III only (presegemental). Lateral fringe extends from anterior border of segment III to anterior third of segment VIII (Fig. 12 , lf).

Case.

Length 9.5-12.3 mm (N = 6); curved, conical (width at anterior opening 2.9-3.4 mm, at posterior opening 1.6-2.5 mm), consisting of mineral particles (sand grains and mica flakes of mixed size; Fig. 15 ).

Material examined.

ITALY: Piemonte: near Fondo, 45°30' N, 07°42' E, 1584 m a.s.l., 11 June 2019, S. Vitecek, J. Martini, 1 final instar larva, several adult males; Piemonte: Pian della Battaglia, 45°33' N, 07°39' E, 1403 m a.s.l., 25 July 2019, J. Martini, N. Falk, 4 final instar larvae; Piemonte: Lago del Gias del Prete, 45°31' N, 07°38' E, 2222 m a.s.l., 24 July 2019, J. Martini, N. Falk, 1 final instar larva, 1 male.

Figures

Figures 1 - 3. Drusus dudor Olah, 2017, 5 th instar larva. 1 Head, dorsal view (a: antenna; numbers refer to setal positions) 2 Head, ventral view (numbers refer to setal positions) 3 Head and prothorax, right lateral view (a: antenna; c: lateral carina; dr: dorsal ridge; m: mandible; numbers refer to setal positions). Scale bars: 0.5 mm.

Figures 4 - 11. Drusus dudor Olah, 2017, 5 th instar larva. 4 Head, thorax and abdominal segment I, dorsal view (dp: dorsal protuberance; lp: lateral protuberance; sa 1, sa 2, sa 3: metanotal setal areas 1, 2 and 3) 5 Head and pronotum, frontal view (arrows: long dark setae not reaching dorsal midline; smo: smooth outline of pronotal ridge; numbers refer to setal positions) 6 Prosternum, ventral view (ph: prosternal horn; ps: prosternite) 7 Left fore leg, anterior view 8 Left mid leg, anterior view (arrows: proximodorsal setae) 9 Left hind leg, anterior view 10 Lateral protuberance, right lateral view (bracket: anterolateral setae; number 5 refers to setal position) 11 Abdominal sternum I, ventral view. Scale bars: 0.5 mm.

Figures 12 - 17. 12 - 15. Drusus dudor Olah, 2017, 5 th instar larva. 12 Abdominal segments VII-IX, right lateral view (lf: lateral fringe; pls: posterolateral seta; ds: dorsal seta) 13 Abdominal segment IX, dorsal view 14 Tip of abdomen, posterior view 15 Larval case, right lateral view 16 Drusus macedonicus Schmid, 1956, 5 th instar larva, head, thorax and abdominal segment I, ventral view (fb: filtering bristles, dotted oval: filtering bristles on hind femur) 17 Drusus muelleri McLachlan, 1868, 5 th instar larva, head, pro- and mesothorax, right lateral view (arrow: mandibles with terminal teeth). Scale bars: 0.5 mm.

Figures 58 - 63. Drusus dudor Olah, 2017, male genitalia. 58 Tip of abdomen, left lateral view 59 Tip of abdomen, posterior view 60 Tip of abdomen, dorsal view 61 Tip of abdomen, ventral view 62 Apex of aedeagus and parameres (arrow: dorsal tooth of parameres) 63 Detail of paraproct, dorsal view (dotted ovals: basolateral bulges). Scale bars: 0.5 mm (except Fig. 63: 0.1 mm).