The nymphs of Sigara ( Tropocorixa ) denseconscripta ( Hemiptera , Heteroptera , Corixidae )

The nymphal instars I and III–V of Sigara (Tropocorixa) denseconscripta (Breddin, 1897) are figured and described in detail, for the first time, with emphasis on morphometry and chaetotaxy of selected structures. The useful characters to identify the nymphal instars and the nymphs of the species of Sigara are provided.

nymphs with the adults and supporting the identification of the species.The taxonomic descriptions of the nymphs were performed using a stereomicroscope (at magnifications up to 144X).For each nymph only differences with the previous nymph description are emphasized.Some specimens were cleared in lactic acid for several days, dissected, and mounted on glass slides in polyvinyl-lacto-glycerol.Observations (at magnifications up to 1000X) and drawings were made using a compound microscope equipped with a drawing tube.Drawings were scanned and digitally edited.
Abdomen.Posterior margins of the segments: I-VII concave medially (dorsal and ventrally), and VIII straight to slightly concave medially (dorsal and ventrally).G3/D3: 6-7, G4/D4: 9-11, and G5/D5: 9-10.Spiracles visible on segments I-VIII, small and rounded; located ventro-laterally near posterior margin (I) or ventrally near anterior margin (II-VIII) of each segment; the one on segment I is bigger than the others abdominal spiracles.Terga with few short, slender setae, and abundant chloride cells.Lateral spines of the abdominal segments (right side): I, zero; II-III, one short; IV, zero or one short, one long; V-VI, three short, one long; VII, four short, one long; VIII, three short, five or six long.Sterna with few short, slender setae, and chloride cells.Central spines on urosternites: I-IV: zero; V: two or three (zero or one short, two long); VI: three (zero or one short, two or three long); VII-VIII: two long.
Second nymph.No specimens were available for study.

Fourth nymph
Similar to third instar except for the following features: Color.Abdominal terga I-II and VIII with one pale marking and III-VII with a pale marking on each side of the notum.

DISCUSSION
The main characters separating the nymphal instars I and III-V of Sigara denseconscripta are (Tabs I, II): the body, head, antenna, pterothorax and legs lengths; the body, head, and eye widths; the number of transverse sulcations of the rostrum; the number of campaniform sensilla on posterior surface of the protrochanter; the number of setae on the inner surface of the protibiotarsus; number of spines on the tibial comb of the protibiotarsus and metatibia; the number of campaniform sensilla on anterior and posterior surfaces of the mesotrochanter; the number of spines on anterodorsal and anterior surfaces of the meso-and metafemora, respectively; the number of long, slender setae on posterior and posterodorsal surfaces of the mesotibia and mesotarsus, respectively; the number of spines on the posteroventral surface of the mesotibia (single and apically serrate); the number of campaniform sensilla on posterior surface of the metatrochanter; the number of spines and long, slender setae on the anteroventral surface, and the number of long setae on the posterior surface of the metatibia; the number of swimming hairs on anteroventral and posterodorsal surfaces of the metatarsus; and the grade of development of the wing pads.In addition, the nymphs of Sigara denseconscripta can be separated on the basis of the presence (instars III-V) or the absence (instar I) of: a basal hydrophobic setose area on the anterior and posterior surfaces of the profemur, and on the anterior surfaces of the meso-and metafemora; a transversal basal row of long slender setae on posterior surfaces of the meso-and metafemora; and a prebasal set of short and stout spines on the anterior surface of the metacoxa (Tab.II).Besides, the last three nymphal instars of S. denseconscripta can be distinguished by the coverage of the basal hydrophobic setose area on posterior surface of the profemur (2/3, instar III; 3/4, IV; 5/6, V).
The last three nymphal instars of Sigara denseconscripta, S. santiagiensis, S. schadei, and S. tucma can be separated from each other based on: the hydrophobic setose area on anterior surface of the profemur covering the basal half of the segment (S. denseconscripta, S. santiagiensis and S. tucma) or more than the basal half (S. schadei); the hydrophobic setose area on posterior surface of the profemur covering the basal half of the segment (S. santiagiensis) or more detailed descriptions and re-descriptions (including chaetotaxy) of the nymphs of this genus.Besides, future works should focus on providing useful morphological data, which with molecular data, will improve the resolution of the analyses of the phylogeny of the Corixidae.