The larva of Drusus bolivari (McLachlan, 1880)(Trichoptera: Limnephilidae: Drusinae)

R. VIEIRA-LANERO, M. A. GONZALEZ & F. COBO

University of Santiago de Compostela, Santiago de Compostela, Spain

AbstractThe hitherto unknown fifth instar larva of Drusus bolivari (McLachlan, 1880) is described for the firsttime and compared with other known similar Iberian species. The most important features areillustrated, and some zoogeographical and ecological notes are included. The thick pronotal ridge ofD. bolivari is the main character to clearly distinguish this larva from those of the remaining knownIberian species of this genus. The most similar larva is that of Anomalopterygella chauviniana (Stein,1874), but a deep dorsomedian gap occurs in the pronotal ridge of D. bolivari that is absent in that ofA. chauviniana.

Keywords: Trichoptera, Limnephilidae, Iberian Peninsula, Drusus bolivari, immatures, larva

Introduction

The subfamily Drusinae Banks 1916 is widely distributed throughout Europe, reaching the

Caucasus and Iran. Nine species were so far cited from the Iberian Peninsula (Gonzalez et al.

1992; Terra 1994; Sipahiler 1992) belonging to four genera: Anomalopterygella Fischer, 1966

(one species); Drusus Stephens, 1837 (six species); Ecclisopteryx Kolenati, 1848 (one

species), and Metanoea McLachlan, 1880 (one species). The last (fifth) instar larvae of

Anomalopterygella chauviniana (Stein, 1874), Drusus annulatus (Stephens, 1837), D. discolor

(Rambur, 1842), D. rectus (McLachlan, 1868), and Ecclisopteryx guttulata (Pictet, 1834) have

been described and/or figured in several papers (see Table I). The larvae of Drusus berthelemyi

Sipahiler, 1992, D. bolivari (McLachlan, 1880), D. cantabricus Schmid, 1956 and Metanoea

malicky Sipahiler, 1992, are still unknown.

A list of the morphological features for the identification of larval Limnephilidae and for

the separation of the subfamily Drusinae has been presented by Waringer (1985). The

larvae of this subfamily live in running waters, mainly in the crenon and rhithron. They are

typical scrapers, with toothless, shovel-shaped mandibles, very suitable for feeding on

ephilitic algae.

We follow in this paper the setal nomenclature and larval terminology proposed by

Williams and Wiggins (1981) and Wallace et al. (1990).

Correspondence: Rufino Vieira Lanero, Dpt. de Biologıa Animal Zoologıa, Facultad de Biologıa, Universidad de Santiago de

Compostela, 15782 Santiago de Compostela, Spain. E-mail: barufo@usc.es

Aquatic Insects

June 2005; 27(2): 85 – 93

ISSN 0165-0424 print/ISSN 1744-4152 online ª 2005 Taylor & Francis

DOI: 10.1080/01650420512331390672

Material and methods

Material examined

48 last instar larvae and six mature pupae of D. bolivari. The specimens were collected from

the following Galician localities (NW Spain): Cabanas Vellas (a creek in Serra de Ancares,

UTM 29T672547425, 1200 m a.s.l.); Fonte de Bois (a spring in Serra de Ancares, UTM

29T673547425, 1500 m a.s.l.); Moreda (a creek in Serra do Caurel, UTM 29T654547215,

700 m a.s.l.); Os Cabaninos (Rıo Ortigal. Serra de Ancares, UTM 29T673547435, 1000 m

a.s.l.); Rıo da Vara (UTM 29T672547415, Serra de Ancares, 1250 m a.s.l.); Rıo da Vega

(UTM 29T675547775, Serra de Ancares, 1100 m a.s.l.). For specific determination of the

aquatic stages, six larval exuviae collected from mature laboratory-reared pupae with distinct

genitalia were examined, thereby ensuring the association between larval and adult

specimens.

The measurements, in millimetres, are given as a range; 15 last instar larvae (n¼ 15) and 20

cases (n¼ 20) of D. bolivari were measured. Both larvae and pupae are preserved in alcohol

and deposited in the Insect Collection of the Department of Animal Biology (University of

Santiago de Compostela, A Coruna, Spain).

Description of the final instar larva

Body length 11.1 – 12.1 mm. General colour of the sclerotized surfaces in dorsal view dark

brown, almost black.

Head capsule (Figures 1 and 6): Length: 1.5 – 1.6 mm; width: 1.6 – 1.7 mm. Almost round

in dorsal view, but flattened dorsally and with an angled occipital edge in lateral view

(Figure 2). Dorsal side dark brown, with a light area around the eyes, ventral side lighter.

A group of spinules surrounds the insertion point of seta 15. Setal arrangement as in

Figures 1, 2, 5, and 6.

A faint carina extends from the oral edge laterally to the eye; the antenna is situated halfway,

slightly closer to the eye. Mandibles without teeth along edges; also no ridges in the central

concavity. The ventral apotome (Figure 3) is triangular and elongated. The submental

sclerites are rhomboidal in shape and with a distal seta.

Thorax: Pronotum (Figures 1, 4, 5, 6) dark brown in colour and with a thick dorsal ridge or

carina extending transversally from the posterodorsal to the anteroventral part of the

pronotum, delimiting an anterior semicircular area. The ridge of every hemipronotum ends

before the midline, resulting in a deep, central gap in frontal view (Figure 6). Ventral side with

Table I. Larval descriptions of the known Iberian Drusinae.

Species Decribed and/or figured by

Anomalopterygella chauviniana

(Stein, 1874)

Decamps & Pujol, 1975; Pitsch, 1993; Waringer & Graf, 1997.

Drusus annulatus (Stephens, 1837) Lestage, 1921; Nielsen, 1942; Hanna, 1961; Hickin, 1967; Hiley, 1970;

Steinmann, 1970; Hiley, 1976; Szczesny, 1978; Wallace, 1980; Sedlak,

1985; Wallace et al., 1990; Waringer & Graf, 1997.

D. discolor (Rambur, 1842) Lestage, 1921, Lepneva, 1966; Steinmann, 1970; Decamps & Pujol, 1975;

Szczesny, 1978; Moretti, 1983; Sedlak, 1985; Bohle, 1987; Waringer,

1987; Waringer & Graf, 1997.

D. rectus (McLachlan, 1868) Decamps & Pujol, 1975.

Ecclisopteryx guttulata (Pictet, 1834) Szczesny, 1978; Wallace et al., 1990; Pitsch, 1993; Waringer & Graf, 1997.

86 R. Vieira-Lanero et al.

a small prosternal horn, and with a posterior prosternite (trapezoidal, with its posterior and

lateral margins dark in colour) with two smaller and dark prosternites at each side.

Setal arrangement on pronotum as in Figures 1, 4 and 6. Frontal margin of the pronotum

with two rows of minute setae and six long setae. In front of the dorsal ridge, several minute

setae are scattered all over the dorsal surface. The back side of the ridge (Figure 4) has only

small and minute setae, mainly inserted on the lateral surface; the anterior border of the ridge

has five large and stout setae on each side. The anterior corner has four stout setae and several

smaller setae.

The mesothorax (Figures 1 and 5) is dorsally covered by a pair of flattened sclerites.

Ground colour of the mesodorsal sclerites brown, but lighter than pronotum; posterior third

even lighter. Setal arrangement as in Figure 1.

Metadorsum (Figures 1 and 5) with six sclerites. Metadorsal anterior-median sclerites

subrectangular and with a dark anterior border, their maximum width is distinctly larger than

the distance between them. A group of 20 – 30 setae is inserted on each of those sclerites.

Posterior metadorsal sclerites triangular and with 11 – 17 setae. A row of 15 – 20 setae is

inserted in the soft cuticle between the posterior sclerites. Lateral metadorsal sclerites with a

small dark spot and densely covered by setae (16 – 20 setae) on the anterior half. On the soft

cuticle, a group of 12 – 24 setae is present between the posterior and lateral sclerites, and

11 – 20 setae are inserted along the anterodorsal margin of the lateral metadorsal sclerites.

Figures 1 – 4. Drusus bolivari (last instar larva). 1, thorax and head in dorsal view; 2, head, lateral view, 3, ventral

apotome; 4, pronotum, lateral view (ornamentation not figured).

The larva of Drusus bolivari (Trichoptera: Limnephilidae) 87

Meso- and metaventer with a posterior row of 5 – 6 pairs of small, rounded or more or less

transversally elongated sternites (Figure 13). Pro-, meso- and metaventer with a small, lateral

seta on either side.

Legs (Figures 7–10) light brown, lighter than pronotum. Ventral edge of prothoracic femur

(Figure 7) with a row of 5 – 6 thick, transparent setae. Two brush setae are inserted on the

anterior side of the prothoracic coxa, but only one on the inner side of the trochanter of the

same leg (Figure 8). Anterior and posterior faces of all femora covered by tiny setae: 6 – 8

setae on hind femur, 4 – 5 on middle and 4 – 5 on first femur. Pro-, meso-, and metathoracic

Figures 5 – 6. Drusus bolivari (last instar larva). 5, head and thorax, anterolateral view; 6, head and pronotum, frontal

view (cephalic ornamentation not figured).

88 R. Vieira-Lanero et al.

tibiae without dorsoproximal setae, but with four dorsodistal setae. Mesoventral distal margin

of tibiae with two spurs.

Mesopleurite ventral process without any setae; metapleurite ventral process with 22 – 26

setae (Figure 5).

Abdomen

Dorsal protuberance of segment I (Figures 12 and 15) with an anterior row of setae and one

posterolateral seta. Lateral protuberances (Figure 15) with an anterior group of setae. Setal

Figures 7 – 10. Drusus bolivari (last instar larva). 7, prothoracic leg, posterior side, 8, anterior side of prothoracic coxa,

trochanter, femur and tibia; 9, mesothoracic leg, posterior side; 10, metathoracic leg, posterior side.

The larva of Drusus bolivari (Trichoptera: Limnephilidae) 89

arrangement in the first abdominal venter as in Figure 14. Lateral fringe present from anterior

margin of abdominal segment III to the first third of segment VIII. No lateral fringe is

observed on segment II, but one dark seta is inserted at the same level on the anterior margin

of this segment.

Tracheal gills of single filaments only. Anterodorsal gills (AD) present on segments II–VII

(sometimes also on VIII); posterodorsal gills (PD) on segments II–V (sometimes also on VI);

anterolateral dorsal gills (ALD) on segments II – IV; anteroventral gills (AV) and poster-

oventral gills (PV) on segments II – VII, and posterolateral ventral gills (PLV) only on

segments II and III.

Segments II – VII with a ventral area of chloride epithelia of elliptic shape. Ventral setae of

abdominal segments very small, dorsal setae longer. Dorsum of segments II – VII with a long

primary seta in sa2 (setal area 2; see Williams & Wiggins, 1981), and a small, hyaline seta both

in sa1 and sa3. Dorsal setae of the segment VIII with similar arrangement but sa2 with a row

of three setae (the outermost the longest), inserted in the posterior part of the segment.

Ventral side of segment IX with a small dark seta on either side.

Posterior margin of ninth abdominal dorsal sclerite (Figure 16) with eight long black setae,

all of them similar in length. Additionally, near the posterior margin (in front of the before-

mentioned setae) the dorsal sclerite bears a group of eight small setae, and a small hyaline seta

is also inserted in the anterolateral margin. Muscle attachment spots slightly visible in the

anterior part of the sclerite. Ninth abdominal dorsum with one posterolateral seta on each

side.

Lateral sclerites of anal prolegs (Figure 16) with four posterior long and strong setae (two of

them longer and stouter); lateral surface covered with 12 – 20 small setae. Ventral side of anal

proleg with 2 – 4 small setae on soft cuticle near anal slit. Anal claws with a small dorsal

accessory claw.

Case

Larval case (Figure 11) slightly curved, conical in shape, made of mineral particles; length

11.3 – 13.1 mm. Posterior opening partially obturated by small mineral particles, but with a

small central opening.

Discussion

The fifth instar larvae of D. bolivari and A. chauviniana can be separated immediately from all

other known Iberian Drusinae larvae by a prominent pronotal ridge. Moreover, this character

also clearly distinguishes the last instar larvae of D. bolivari and A. chauviniana from those of

the remaining known Iberian Limnephilidae.

The fifth instar larvae of A. chauviniana and D. bolivari are very much alike. In this study we

have compared the larvae of D. bolivari with 36 larvae of A. chauviniana, all of them collected

in Galician rivers. The extent of the pronotal ridge is the main diagnostic character to clearly

distinguish the larvae of D. bolivari from those of A. chauviniana. The hemipronotal ridges of

A. chauviniana are fused in the dorsal line (cf. Pitsch, 1993, Figures 228, 252, 261), but in

D. bolivari they are clearly separated by a gap (Figure 6). In addition, the posterior surface

of the ridge is very uniform in A. chauviniana (cf. Decamps & Pujol 1975; Pitsch, 1993,

Figures 252 and 255; Waringer & Graf 1997), while two hollows are present in the rear face in

D. bolivari (Figures 1 and 5).

Additionally, the cephalic capsule of A. chauviniana (cf. Pitsch 1993, Figure 228; Decamps

& Pujol 1975, Figure 2) is slightly wider in comparison with its length than that of D. bolivari,

90 R. Vieira-Lanero et al.

and has a rounded occipital region, while the larval head of D. bolivari is slightly flattened

dorsally, so that the occipital region is angled in lateral view (Figure 2).

Some differences were also observed in the anteromedian metathoracic sclerites,

relatively longer and darker in D. bolivari (Figure 1) than in A. chauviniana (cf.

Decamps & Pujol 1975). Additionally, the pigmentation of the lateral metadorsal sclerites

is darker in A. chauviniana (cf. Decamps & Pujol 1975; Waringer & Graf 1997) than in

D. bolivari.

The thoracic legs of A. chauviniana (cf. Decamps & Pujol 1975; Waringer & Graf;, 1997)

are normally darker than those of D. bolivari; the prothoracic femora of A. chauviniana bear

four strong and hyaline ventral setae (5 – 6 in D. bolivari) and the dorsal margin of all tibiae is

completely covered by setae, whereas those setae are confined to the distal edge in D. bolivari

(Figures 7, 9 and 10).

Finally, the dorsal protuberance of the first abdominal segment of A. chauviniana is

completely surrounded by setae, whereas in D. bolivari only two setae are inserted at its side

(Figure 12).

Figures 11 – 16. Drusus bolivari (last instar larva). 11, case, lateral view; 12, first abdominal dorsum; 13, mesosternites;

14, first abdominal venter; 15, first abdominal segment, lateral view; 16, ninth abdominal segment and anal prolegs,

dorsal view.

The larva of Drusus bolivari (Trichoptera: Limnephilidae) 91

Notes on biology, ecology and distribution

Most of the specimens studied were collected in a small, clean mountain brook (Sierra de

Ancares, Lugo) of almost 1 m width and strong slope, with small waterfalls. The species has

been reported from many localities from 700 to 1500 m a.s.l. and its flight period extends

from July to September (Gonzalez 1988). According to Gonzalez et al. (1992), D. bolivari has

been dispersedly cited from many localities throughout the Iberian Peninsula, and also from

the Pyrenees and France (Vincon, 1987).

Acknowledgements

This study was supported by PGIDT 01PXI20002PR of Xunta de Galicia.

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