Journal of Insect Science RESEARCH Description of the Immature Stages of Sigara (Aphelosigara) tucma S. A. Konopko1,2,3 1Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Divisio´n de Entomologı´a. Av. Angel Gallardo 470, C1405DJR, Buenos Aires, Argentina 2Consejo Nacional de Investigaciones Cientı´ficas y Te´cnicas (CONICET), Av. Rivadavia 1917 (C1033AAJ), Buenos Aires, Argentina 3Corresponding author, [email protected] Subject Editor: Michael Heethoff J. Insect Sci. 14(186): 2014; DOI: 10.1093/jisesa/ieu048 ABSTRACT. Descriptions of the last three nymphal instars of the water boatman Sigara (Aphelosigara) tucma Bachmann (Hemiptera: Heteroptera: Corixidae) are provided, for the first time, for specimens collected in northern Argentina; the egg is redescribed. Adults and nymphs were collected in the field. The eggs were obtained by dissection from females. The immature stages were fixed for micro- scopic examination and illustration and were described with an emphasis on morphometry and chaetotaxy of selected structures. The last three nymphal instars of S. tucma can be easily recognized by the body and head lengths and widths; the number of transverse sul- cations of the rostrum; the chaetotaxy of trochanters, protibiotarsus, midlegs, metatibia, and metatarsus; and the grade of develop- Downloaded from ment of the wing pads. The eggs of the genus Sigara can be distinguished by the size and the chorionic surface. The chaetotaxy of the mesonotum, metafemur, and metatibia distinguish groups of species belonging to the last nymphal instar of the genus Sigara. A key to the last three nymphal instars of the species of Sigara from Argentina is provided. Key Words: Heteroptera, Corixidae, egg, nymph, chaetotaxy http://jinsectscience.oxfordjournals.org/ The cosmopolitan genus Sigara Fabricius (Hemiptera: Heteroptera: 1969); and the last three nymphal instars of S. (Subsigara) fossarum, Corixidae) includes 70 species in America of medium- to large-sized S. (S.) scotti, S. (S.) falleni, S. (S.) distincta, S. (Sigara) striata, S. (S.) water boatmen (Morrone et al. 2004). Sigara is placed within the tribe semistriata, S. (S.) limitata, S. (S.) nigrolineata, S. (S.) lateralis), and S. Corixini, subfamily Corixinae and is divided into various subgenera (Sigara) janssoni Lucas (Jansson 1969; Lo´pez et al. 1996). Melo and (Hungerford 1948a). The genus Sigara is represented in Argentina by Scheibler (2011) presented descriptions of the five nymphal instars of 18 species, 17 belonging to the subgenus Tropocorixa Hutchinson and S. (Tropocorixa) jensenhaarupi Jaczewski. All the species mentioned one to the subgenus Aphelosigara Hungerford (Bachmann 1981). The above were treated very superficially and were not described in detail, immature stages of S. (Aphelosigara) tucma Bachmann are studied in making comparisons difficult. Recently, Konopko (2012, 2013b) the present contribution. described in detail the five nymphal instars of two species of Sigara The genus in America is distributed from Canada to southern (S. (Tropocorixa) schadei (Hungerford) and S. (T.) santiagiensis Argentina, in Santa Cruz Province and Malvinas Islands (Hungerford (Hungerford)) with an emphasis on morphometry and chaetotaxy. by guest on January 22, 2015 1948a; Bachmann 1960, 1961b, 1962a, 1979; Hungerford and Matsuda Thus, the last two works and this contribution attempt to study the nym- 1961; Contartese and Bachmann 1986; Arnett 1993; Morrone et al. phal morphology of Sigara in a broader sense, based on comparative 2004). S. tucma is only known from a few localities in Argentina (from approach. Salta to Co´rdoba Provinces) (Bachmann 1981; Morrone et al. 2004). It The main goals of this contribution are: 1) to redescribe the egg and seems to be frequent in small lentic water bodies with moderate to describe and illustrate, for the first time, the last three nymphal instars amounts of submerged vegetation (aquatic mosses mainly), at altitudes of S. tucma, including a detailed morphometric and chaetotaxic analysis of 1,500 m a.s.l. in the mountains of northwestern Argentina of selected structures, (2) to compare the eggs and the nymphs of the (Bachmann 1981). species of Sigara described up to the moment, 3) to establish the nym- The systematics of the adults of Sigara were studied by Hutchinson phal characters useful in identifying instars and species of Sigara, and (1940), Hungerford (1948a), and Bachmann (1960, 1961a,b, 1962a–d, 4) to provide an identification key to the last three nymphal instars of 1963, 1966, 1979, 1981, 1987), and they are comparatively well the species of Sigara from Argentina. known, but there are few descriptions of the immature stages available in the literature. Only the eggs of 12 species of Sigara have been de- Material and Methods scribed (Poisson 1933; Hungerford 1948b; Fernando 1965; Bachmann Adults and nymphs of S. tucma have been collected in the field, 1981; Konopko 2012, 2013b). According to the nymphs, there are brief fixed, and preserved in 96% ethanol. The eggs were obtained by dissec- descriptions of the first nymphal instar emphasizing the chaetotaxy of tion from females. The material is held in the collection of the Divisio´n European species of Sigara: S. (Sigara) concinna (Fieber), S. (S.) later- de Entomologı´a, Museo Argentino de Ciencias Naturales ‘Bernardino alis (Leach), S. (S.) striata (L.), and S. (Subsigara) falleni (Fieber) Rivadavia’ (MACN), Buenos Aires, Argentina. (Cobben and Moller Pillot 1960); the last nymphal instar of Sigara The taxonomic descriptions of the eggs and nymphs were per- (Subsigara) fossarum (Leach), S. (S.) scotti (Douglas & Scott), S. (S.) formed using a Leitz stereomicroscope (at magnifications up to 144Â). falleni, S. (S.) distincta (Fieber), S. (Sigara) striata, S. (S.) dorsalis For each nymph only differences with the previous nymph description (Leach), S. (S.) semistriata (Fieber), S. (S.) venusta (Douglas & Scott), are emphasized. Some nymphal specimens were cleared in lactic acid, S. (S.) limitata (Fieber), S. (S.) lateralis, S. (S.) nigrolineata (Fieber), dissected, and mounted on glass slides in polyvinyl-lacto-glycerol. S. (S.) concinna, S. (S.) stagnalis (Leach), S. (S.) selecta (Fieber), and Observations (at magnifications up to 1,000Â) and drawings were S. (S.) hellensi (Sahlberg) (Cobben and Moller Pillot 1960; Nieser made using an Olympus CX31 compound microscope equipped with a VC The Author 2014. Published by Oxford University Press on behalf of the Entomological Society of America. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact [email protected] 2 JOURNAL OF INSECT SCIENCE VOLUME 14 drawing tube. Drawings were scanned and digitally edited. The key to S. Mazzucconi coll. (MACN); National Park El Rey, ditch that empties identify the last three nymphal instars of the species of Sigara is based in Sala stream, 1 instar III, 9 instar IV, 3 instar V, 10.XI.2003, S. on the Argentinean species described up to now. Mazzucconi coll. (MACN). Tucuma´n Province: San Javier, 15.III.1961 and 18–28.I.1971, 23 dissected eggs, A. Bachmann coll. Morphometric and Chaetotaxic Analysis (MACN) (Figs. 1–24; Tables 1–3). Alcohol-preserved material was observed in a Petri dish with 96% Egg (Figs. 1 and 2; n ¼ 10) ethyl alcohol. Nymphal structures were measured utilizing a Leitz stereo- Egg length (EL): 0.58–0.63 mm. Egg width (EW): 0.49–0.54 mm. microscope equipped with a micrometric ocular. Paired structures of each Micropyle length: 0.03–0.04 mm. Stalk length: 0.05 mm. Oval shape individual were considered independently. The interpretation of the chae- (Fig. 1), EL/EW: 1.16–1.24, flattened at one side, with a very short stalk totaxy of the legs follows the one stated in Konopko et al. (2010a). (Fig. 1). Color yellow, stalk transparent. Chorionic surface ornamented The following material was measured: eggs, 10; instar III, one speci- by smooth hexagons (Fig. 2). men; and instars IV–V, five specimens each (Table 1). The chaetotaxy First and second nymphal instars. No specimens were available of the following material was studied: instar III, one specimen; and in- for study. stars IV–V, five specimens each. Figures 15–16, 18–19, and 21–22 Third nymphal instar (Figs. 3–4, 9, 15, 18–19, 21–22; n ¼ 1) show the position of spines, setae, and bristles on the legs. Color. Ground color testaceous with dark markings. Head testa- ceous with dark markings, except ecdysial line and ventral and lateral Results surfaces testaceous; posterior margin dark. Eyes reddish brown. Rostrum testaceous, except dark apically. Antennae testaceous with Sigara (Aphelosigara) tucma. pale setae. Pronotum testaceous. Mesonotum testaceous, with dark se- Material Examined. Argentina. Salta Province: pothole on route tae on anterior half of the segment. Metanotum with a pale eye shaped Downloaded from 19, near Aguas Blancas, 1 instar IV, 7 instar V, 19.XI.2003, marking on each side of the notum, near the anterior margin of the seg- ment, which joins to a medial pale inverted triangle marking, near the posterior margin of the segment, forming between the three a single pale marking. Thoracic pleurae and sterna testaceous. Legs testaceous. Table 1. Measurements (in mm) of nymphal instars III–V of Abdominal terga I–VII dark with pale markings, and abdominal tergum http://jinsectscience.oxfordjournals.org/ S. (Aphelosigara) tucma VIII testaceous; scent glands reddish brown on segments IV and V; ab- Measure Instar III Instar IV Instar V dominal sternites testaceous, except last segment with a rounded, mid- BL 2.18 3.50–3.60 4.61–5.03 dle, dark area. Connexivum testaceous with dark markings on posterior BW 1.34 1.81–1.88 2.28–2.43 margin of each segment. HL 0.50 0.74–0.77 0.97–0.99 Body.