The larva of Drusus vinconi Sipahiler, 1992 (Trichoptera, Limnephilidae, Drusinae)

Abstract This paper describes the previously unknown larva of Drusus vinconi Sipahiler, 1992. Information on the morphology of the 5th larval instar is given, and the most important diagnostic features are illustrated. In the context of existing identification keys the larva of Drusus vinconi keys together with Drusus annulatus (Stephens, 1837), Drusus biguttatus (Pictet, 1834), Drusus ingridae Sipahiler, 1993, Hadimina torosensis Sipahiler, 2002 and Leptodrusus budtzi (Ulmer, 1913). These species differ in the contours of the pronotum in lateral view, the presence/absence of the pronotal transverse groove, the shape of the median notch of the pronotum (in anterior view), pronotal sculpturing, presence/absence of the lateral carina of the head capsule, the number of proximo-dorsal setae on the mid-and hind femora, where the lateral fringe starts on the abdomen, and in geographic distribution. With respect to zoogeography, Drusus vinconi is a (micro-)endemic of the Western Pyrenees. The species prefers stony substratum in springs and springbrooks of the montane and subalpine region (Graf et al. 2008; Sipahiler 1992, 1993). As a grazer, the larvae of Drusus vinconi feed on biofilm and epilithic algae.


Material and methods
Hand nets were used to collect larvae and adults of Drusus vinconi in and beside a small stream about 7 km SW of the ski area Arette La Pierre Saint Martin, Département Pyrénées-Atlantiques, Midi-Pyrénées, France (42°57'17.67"N, 0°49'26.91"W) on 23 July 2012 (leg. W. Graf ). The material was preserved in 90% ethanol. A Nikon SMZ 1500 binocular microscope with DS-Fi1 camera and NIS-elements D 3.1 image stacking software for combining 8-50 frames in one focused image were used to study and photograph the larvae.
Species affiliation was enabled by the fact that putative Drusus vinconi larvae were collected close to their locus typicus where the only other Drusinae larvae present, D. discolor (Rambur, 1842), are clearly different from the species in question by their dense hair cover on head and pronotum. In addition, adults of both sexes of D. vinconi were collected at the same sites as the unknown larvae.

Description of the 5th instar larva of Drusus vinconi
Biometry. Body length of 5th instar larvae ranging from 9.7 to 10.8 mm, head width from 1.76 to 1.90 mm (n = 2).
Legs light brown with numerous setae on coxae, trochanters, and femora; tibiae and tarsi sparsely setose. Femora with several proximodorsal setae (e.g. Fig. 8, black bracket), and with setation on anterior and posterior faces; fore femora with 4, mid and hind femora with 3 yellow ventral-edge setae; no minute spines along ventral edges present. Foreleg coxa, femur and tibia wider than those of mid-and hind legs. Fore and mid trochanters with setae only on proximal sections; fore trochanters additionally with distal ventral trochanteral brush. Mid-and hind tibiae with dorsal setae only on distal 3rd (Figs 8, 9).
Abdomen. Abdominal segment I with 1 dorsal and 2 lateral fleshy protuberances (Figs 4, 10). Continuous transverse row of setae present anterior of dorsal protuberance (comprising fused setal areas sa1, sa2, sa3, sensu Wiggins 1998), stretching laterally from dorsal sections of lateral protuberances; posterior of dorsal protuberance, another row of setae present (Fig. 4). All these setae with small basal sclerites. Lateral protuberances without posterior sclerites (Fig. 10). Anterior of each lateral protuberance a continuous band of anterolateral setae connected to each dorsal and ventral sa3 setal group (Fig. 10). Abdominal sternum I with fused setal areas sa1, sa2 and sa3, creating continuous field of setae, therein occurs pair of central large basal sclerites with irregular borders and small number of randomly distributed basal sclerites of smaller diameter (Fig. 6). Abdominal dorsum VIII with 2 long and 2 short posterodorsal setae (pds) (Fig. 11 pds); only 1 posterolateral seta present on each half of abdominal dorsum IX (Fig. 11, arrows). Abdominal dorsum IX bearing beige pentangular sclerite with 8 long and several short setae (Fig. 11). Beige anal prolegs are of limnephilid type with medium brown anal claws, each with 1 small accessory hook (Fig.12).
All gills as single filaments (Fig. 10). Dorsal gills present at most from abdominal segments II-VII (presegmental positions). Ventral gills present from segment II (presegmental) to segment VII (postsegmental). In lateral row, gills present on segments II-III only (ventrolateral position). Lateral fringe extends from anterior border of segment III (Fig. 10 f) to middle of segment VIII.
At this position in the key, Drusus vinconi appears together with D. annulatus, D. biguttatus (Pictet, 1834), D. ingridae, Hadimina torosensis Sipahiler, 2002 andLeptodrusus budtzi. These species are easily distinguished by differences in dorsal profile, presence/absence of the lateral carina on the head capsule, number of proximo-dorsal setae on mid-and hind femora, origin of abdominal lateral fringe, and geographic distribution (Table 1).

Discussion
Drusus vinconi is a (micro-)endemic of the Western Pyrenees. Its locus typicus is situated at the ruisseau de Chousse, a tributary of the Vert d'Arette, near the Serre de Benou, at 1300 m a.s.l. At this site D. discolor was the only other Drusinae species. Larvae of D. discolor are clearly different from D. vinconi larvae by their dense hair cover on the head and pronotum. Adults of D. vinconi are morphologically close to D. monticola McLachlan, 1876. Differences exist in the structure of the male intermediate appendages which are triangular, and in the preanal appendages which are long and ovoid in D. vinconi. The female is characterised by a very short median scale (Sipahiler 1992).
The species was abundant in a small, stony stream near the ski area Arette La Pierre St Martin in the Département Pyrénées-Atlantiques of the Midi-Pyrénées region, France. Drusus vinconi is a rheophilic species inhabiting springs and springbrooks where it can be observed on the surface of boulders and large stones ). According to its mouthpart anatomy, D. vinconi is a grazer, feeding exclusively on epilithic algae and biofilm. Records exist from montane and subalpine sites situated well above 800 m a.s.l. (Sipahiler 1992(Sipahiler , 1993. Adults fly in June and July.