Drusinae, Banks, 1916

Posilović, Hrvoje, 2010, Description of the larvae of Drusus ramae Marinković- Gospodnetić and Drusus medianus Marinković- Gospodnetić (Trichoptera: Limnephilidae) with some genetic, distributional, ecological, faunal and conservation notes, Zootaxa 2484, pp. 1-24 : 13-17

Morphological separation of larvae of Drusus ramae and Drusus medianus from other European Drusinae and identification key for known Drusus larvae from the Balkan Peninsula

Larvae of only 2 endemic species from the Balkan Peninsula have been described previously, D. croaticus and D. radovanovici septentrionis ( Kučinić et al. 2008) . Drusus croaticus , D. ramae , D. medianus and D. radovanovici septentrionis larvae are morphologically very distinct, especially regarding features of the head ( Figs 33–40 , 45 ), pronotum ( Figs 33–36 , 41–44 ) and metanotal sclerites ( Figs. 46–53 ).

Larvae of D. ramae and D. medianus are easily distinguished from each other by the markedly different shape of the pronotum ( Figs 34–35 , 42–43 ). Moreover, larvae of D. medianus have spinules on the head beside the eyes ( Figs. 19–21 , 45 ), while larvae of D. ramae lack this feature ( Figs 34 , 38 ).

The larva of D. croaticus is easily distinguished from the larvae of D. ramae and D. medianus by the following characters: the shape of pronotum ( Figs 33–35 , 41–43 ) ( D. croaticus has a more rounded posterior part of the pronotum and a flattened anterior part), absence of spinules on the head, and absence of prominent black median setae at the anterior border of the pronotum in D. croaticus ( Figs 33 , 37 , 41 ). Similarly, the larva of D. radovanovici serptentrionis is easily distinguished from the larva of D. ramae by the following characters: the shape of the pronotum ( D. ramae has two prominent acute humps lacking in D. radovanovici septentrionis ) ( Figs 34, 36 , 42, 44 ) and presence/absence of head spinules beside the eyes (present in D. radovanovici septentrionis , absent in D. ramae ) ( Figs 34 , 38 ).

D. radovanovici septentrionis is morphologically quite similar to D. medianus but some subtle characters distinguish larvae of these two species: D. medianus bears white recumbent setae on the whole area of the pronotum ( Figs 35 , 43 ), but D. radovanovici septentrionis bears white recumbent setae only on the posterior and lateral parts of its pronotum ( Figs 36 , 44 ). About 10 % of D. radovanovici septentrionis specimens had only a few, small, white recumbent setae anteromesally on the pronotum as opposed to D. medianus larvae that had numerous and longer white setae. In some cases (10–15% specimens), areas with spinules are larger in D. medianus ( Figs 19, 20 , 39 , 45 ) compared to D. radovanovici septentrionis ( Fig. 45 ). Moreover, the area covered with spinules is always compact in D. medianus , whereas some larvae of D. radovanovici septentrionis had only a small number of sparsely distributed spinules ( Fig. 45 , right).

Besides the above mentioned characters, we have found some differences in the shape and size of the anterior-median sclerites of the metanotum that separate those 4 species into 2 distinct groups ( Figs 46–53 ). All 3 species from the D. bosnicus Group have similarly shaped triangular sclerites ( Figs 46–51 ), as opposed to D. croaticus on which they are ellipsoid to quadratic ( Figs 52–53 ). Drusus medianus has the most triangular shape of sclerites ( Figs 48–49 ); those of D. croaticus are more ellipsoid to quadratic, with rounded anterior and posterior margins ( Figs 52–53 ). The shortest distance between sa 1 sclerites was recorded in D. medianus (average = 0.08 mm) and the longest for D. ramae (average = 0.19 mm) ( Tab. 2). The shortest width of sa 1 sclerites was recorded in D. croaticus (average = 0.23) and the longest in D. medianus (average = 0.33) ( Tab.

2). Drusus ramae and D. croaticus showed more similarity in average width of sa 1 sclerites and distance between them, in contrast to D. medianus and D. radovanovici septentrionis ( Tab. 2). Length of the sa 1 sclerites is similar in all 4 species ( Tab. 2). Posteromedian (sa 2) sclerites in the 4 species vary in form and size ( Figs 46–53 ; Tab. 2). The shape and size of sa 1 sclerites are only relatively useful for diagnosis because we found variability among some specimens, especially in species from the D. bosnicus Group ( Figs 46–51 ). Therefore, we recommend stronger reliance on other morphological features: shape of pronotum, area covered with spinules, position of white recumbent setae on the pronotum. Aside from morphological differences, molecular data clearly distinguish larvae of these 4 species ( Previšić et al. 2009).

Subfamily Drusinae is divided into 8 genera: Anomalopterygella , Cryptothrix , Drusus , Ecclisopteryx , Hadimina , Leptodrusus , Metanoea and Monocentra ( Schmid 1956, Sipahiler 2002; in tribe Drusini according to Morse 2010, Vshivkova et al. 2007). Larval morphological features typical for species belonging to this subfamily were well-described by Graf et al. (2005) and Waringer & Graf (1997). The following features clearly distinguish larvae of D. ramae and D. medianus from other described Drusinae genera and species ( Decamps & Pujol 1975, Graf et al. 2005, 2009, Hickin 1967, Lepneva 1966, Kučinić et al. 2008, Pitsch 1993, Sedlák 1980, Szczesny 1978, Urbanič et al. 2003, Vieira-Lanero et al. 2005, Wallace et al. 1990, Waringer 1987, Waringer & Graf 1997, Waringer et al. 2000, 2007a, 2007b, 2008a, 2008b):

• Cryptothrix nebulicola McLachlan, 1867 (distributed in central Europe, Alps); D. alpinus (Meyer-Dür, 1875) (distributed in western Alps), D. chrysotus (Rambur, 1842) (distributed in central Europe, Alps), D. discolor (distributed in Europe), D. franzi Schmid, 1956 (distributed in eastern Alps); D. muelleri McLachlan, 1868 (distributed in Alps) and D. romanicus . (distributed in Balkan Peninsula; Romania, Bulgaria) have teeth along the mesal margin of each mandible; D. ramae and D. medianus don’t have these teeth.

• Drusus discolor and D. romanicus have hair-like structure on the head and pronotum; these structure are absent in D. ramae and D. medianus .

• Drusus monticola McLachlan, 1876 (distributed in eastern Alps), and D. nigrescens Meyer-Duer, 1875 (distributed in western Alps), have different shape of the pronotum in lateral view; these species have a ridge of dorsal humps in the last 1/3rd of the pronotum, whereas D. ramae and D. medianus have the ridge positioned anteriorly.

• Drusus nigrescens has a large, median sclerotized patch on abdominal sternum I (setal bases creating a sclerotized pattern) and lateral fringe started from posterior third of III abdominal segment; D. ramae and D. medianus don’t have this sclerotized patch and lateral fringe started from II abdominal segment.

• Drusus alpinus , Drusus annulatus Stephens, 1837 (distributed in central & western Europe), D. biguttatus (distributed in Europe), D. camerinus Moretti, 1981 (distributed in Apennine Peninsula), D. croaticus (distributed in Dinaric Mountains), D. destitutus (Kolenati, 1848) (distributed in central Europe, Alps), Drusus franzi , D. improvisus McLachlan, 1884 (distributed in Apennine Peninsula), D. mixtus (Pictet, 1834) (distributed in Alps), D. rectus McLachlan, 1868 (distributed in Iberian Peninsula) and Drusus trifidus McLachlan, 1868 (distributed in central Europe) have different shape of the pronotum in lateral view; these species have more rounded posterior part of pronotum, without pronuced hump (humps); D. ramae and D. medianus have a pronuced hump (humps) in this part of the pronotum.

• Drusus trifidus has numerous light spines on pronotum; D. ramae and D. medianus don’t have these numerous spines on pronotum.

• Drusus aprutiensis Moretti, 1981 (distributed in Apennine Peninsula), has a more flattened pronotum in lateral view; D. ramae and D. medianus have a pronounced hump (humps) in posterior part of the pronotum.

• Drusus alpinus , D. aprutiensis , D. camerinus , Drusus carpathicus Dziedzielewicz, 1911 (distributed in Carpathian Mountains), D. croaticus , D. franzi , D. mixtus and D. rectus lack prominent, long median setae dorsally on anterior border of the pronotum; D. ramae and D. medinaus have long, median setae in this part of pronotum.

• Drusus carpathicus lacks dorsal gills on abdomen; D. ramae and D. medianus have these gills.

• Drusus radovanovici septentrionis (distributed in Balkan Peninsula) has only a few, small, white recumbent setae anteromesally on the pronotum; D. medianus has numerous and longer white setae in this part of pronotum, D. ramae have more produced humps in posterior part of pronotum than D. radovanovici septentrionis .

• Anomalopterygella chauviniana (Stein, 1874) (distributed in western Europe), D. bolivari (McLachlan, 1880) (distributed in Iberian Peninsula) and D. brunneus Klapálek, 1898 (distributed in the Carpathian Mountains), have different morphology of posterior part of pronotum; these species have a very pronounced mid-dorsal concavity in the dorsal hump; D. ramae has a more-pointed ridge on each hemipronotum; and the mid-dorsal concavity is nearly absent in D. medianus .

• Drusus destitutus and D. melanchaetes McLachlan, 1876 (distributed in western Alps), have setae through the whole length on dorsal side of mid- and hind-legs tibia; D. ramae and D. medianus don’t have these continuous row of setae.

• Ecclisopteryx dalecarlica Kolenati, 1848 (distributed in Europe), E. guttulata (Pictet, 1834) (distributed in Balkan Peninsula, central and western Europe) and E. madida (McLachlan, 1867) (distributed in central Europe) have prominent spines on head and/or pronotum; D. ramae and D. medianus lack these prominent head and/or pronotal spines.

• Ecclisopteryx asterix Malicky, 1979 (distributed in southern Alps), has ovoidal metanotal anteromedian sclerites (metanotal sa 1 sclerites), different shape of the pronotum in lateral view and lateral fringe started from last third of III abdominal segment; D. ramae and D. medianus have more triangular metanotal anteromedian sclerites and lateral fringe started from II abdominal segment.

• Metanoea rhaetica Schmid, 1956 , and M. flavipennis (Pictet, 1834) have a large, median sclerotized patch on abdominal sternum I, that is lacking in D. ramae and D. medianus .

Identification key of known Drusus larvae from Balkan Peninsula

1 Mandibles each with subapicomesal tooth; head with felt-like hair...................................... D. discolor , D. romanicus

- Mandibles without teeth along mesal margin ............................................................................................................... 2

2 Anterior margin of pronotum without prominent, black median setae; anterior part of pronotum flat, posterior part curved........................................................................................................................................................ D. croaticus

- Anterior margin of pronotum with prominent, black median setae............................................................................. 3

3 Head with spinules........................................................................................................................................................ 4

- Head without spinules................................................................................................................................................... 5

4 Anterodorsal part of pronotum without numerous white, recumbent setae...................................... D. r. septentrionis

- Anterodorsal part of pronotum with numerous white, recumbent setae..................................................... D. medianus

5 Posterior part of pronotum curved ............................................................................................................ D. biguttatus

- Posterior part of pronotum with 2 prominent acute humps ............................................................................ D. ramae

Figures

FIGURES 33 – 36. 33, Drusus croaticus Marinković- Gospodnetić, 1971: head and pronotum protruding from case, right lateral view; 34, Drusus ramae Marinković- Gospodnetić, 1971: head and pronotum, right lateral view; 35, Drusus medianus Marinković- Gospodnetić, 1976: head and pronotum, right lateral view; 36, D. radovanovici septentrionis Marinković- Gospodnetić, 1976: head and pronotum, right lateral view.

FIGURES 37 – 40. 37, Drusus croaticus Marinković- Gospodnetić, 1971: posterior part of the head, right lateral view; 38, Drusus ramae Marinković- Gospodnetić, 1971: posterior part of the head, right lateral view; 39, Drusus medianus Marinković- Gospodnetić, 1976: parietal part of the head at eye level, right lateral view; 40, D. radovanovici septentrionis Marinković- Gospodnetić, 1976: parietal part of the head at eye level, right lateral view.

FIGURES 41 – 45. 41, Drusus croaticus Marinković- Gospodnetić, 1971: pronotum, right lateral view; 42, Drusus ramae Marinković- Gospodnetić, 1971: pronotum, right lateral view; 43, Drusus medianus Marinković- Gospodnetić, 1976: pronotum, right lateral view; 44, D. radovanovici septentrionis Marinković- Gospodnetić, 1976: pronotum, right lateral view; 45, Drusus medianus Marinković- Gospodnetić, 1976 (left), and D. radovanovici septentrionis Marinković- Gospodnetić, 1976 (right): parietal part of the head at eye level showing spinules, right lateral view.

FIGURES 46 – 53. Metanota of Drusus spp., showing anteromedian (sa 1) and posteromedian (sa 2) sclerites. 46 – 47, Drusus ramae Marinković- Gospodnetić, 1976; 48 – 49, Drusus medianus Marinković- Gospodnetić, 1971; 50 – 51, D. radovanovici septentrionis Marinković- Gospodnetić, 1976; 52 – 53, Drusus croaticus Marinković- Gospodnetić, 1971.

FIGURES 16 – 21. Drusus medianus Marinković- Gospodnetić, 1976. 16, larva in its case, right lateral view; 17, larva, right lateral view; 18, head, pronotum and mesonotum, right lateral view; 19, head with spinules above eye, right lateral view; 20, area with spinules, right lateral view; 21, spinules, right lateral view.