Microstigma maculatum Hagen

Neiss, Ulisses Gaspar, Lencioni, Frederico A. A., Hamada, Neusa & Ferreira-Keppler, Ruth Leila, 2008, Larval redescription of Microstigma maculatum Hagen in Selys, 1860 (Odonata: Pseudostigmatidae) from Manaus, Amazonas, Brazil, Zootaxa 1696, pp. 57-62 : 58-62

Microstigma maculatum Hagen in Selys, 1860

(Figures: 2–12)

Larval description (male): length (without gills), 18.2 mm; larva thin with predominant color dark brown (Fig. 2).

Head (length, 2.24 mm, maximum width, 4.2 mm): Almost twice as wide as long (Fig. 2), occiput concave, cephalic lobes prominent and rounded, with a group of spiniform setae on posterior margin. Labrum anterior margin covered with thin setae. Antennae lost during emergence. Mandible: L 1’ 1234 xy ab / R 1’ 1234 0y ab ( Figs. 3–5 ) ( Watson 1956). Maxila as illustrated ( Fig. 6 ). Labium prementum/postmentum articulation surpassing base of front leg. Prementum (length, 2.9; width, 2.4) slightly concave, without premental setae ( Fig. 8 ). Ligula strongly convex and slightly acuminate ( Figs. 8–9 ). Labial palp with four setae longer than the width of palp, plus a fifth insertion point anteriorly to more basal setae ( Figs. 7 and 11 ). A group of short and thin setae on outer basal margin of palp. Two terminal teeth, the superior short and truncated, the inferior longer and pointed, with apex slightly curved ( Fig. 7 ). Movable hook well developed with apex slightly incurved.

Thorax: Pronotum with two dorsal tuberculate shaped protuberances, one on each side of midline; posterior angle rounded with short and thin setae. Pterothorax lacking spots or projections. Anterior and posterior wing pads similar in shape and length (anterior wing pad length, 7 mm, posterior, 6.65 mm), both reaching middle of fourth abdominal segment (Fig. 2). Legs with femur, tibia and dorsum of tarsi with thin setae along their extension. Hind femur length, 3.9 mm; hind tibia length, 4.2 mm. Latero-ventral region of tibia with groups of spiniform setae apically, including some tridentate ones, especially on middle and hind legs. Tarsi tri-segmented, each with two ventral rows of tridentate setae, these more evident on the first tarsal segment.

Exuvia of Microstigma maculatum , male (antennae lost during emergence). (Scale Bar: 2 mm)

Abdomen: Cylindrical, tegument smooth and of uniform color. Posterodorsal edge of last abdominal segment covered with short spines, and with a strong median concavity (Fig. 2). Male gonapophyses short and conical, ending in a pointed projection after a shallow constriction ( Fig. 10 ), not reaching posterior edge of ninth abdominal segment. Gill damaged during adult emergence, except one of the lateral lamellae which was slide mounted using Euparal© medium. Lateral gill dark brown with apex slightly whitish, petiolate, longer than wide (length, 3.2 mm, width, 1.9 mm), foliate and strongly constricted at basal third, petiole well developed with a row of short, spiniform setae on dorsal and ventral margins ( Fig. 12 ).

Material examined. BRAZIL: AMAZONAS: Manaus: urban forest fragment at the Eduardo Gomes International Airport (03º02'31.4" S / 60º04'13.9" W), 1 (male) last-instar larva collected in a fallen tree trunk, 10.v.2005 (emerged in laboratory on 23.xi.2005), Neiss, U. G. leg.

Bionomics and taxonomic discussion. The water of the breeding site accumulated in a hole created by wood decomposition on a fallen tree trunk together with leaves and small branches. On a second visit on 25 November 2005, the same hole was colonized by tadpoles of Osteocephalus oophagus Jungfer & Schiesari, 1995 ( Anura : Hylidae ), a common species in Amazonia known to oviposit in phytotelmata ( Jungfer & Weygoldt 1999; Lima et al. 2006); no other Odonata larvae were found.

The larvae of five of 10 Pseudostigmatidae known from Brazil have been described: Mecistogaster ornata Rambur, 1842 , Mecistogaster asticta Selys, 1860 , Mecistogaster linearis (Fabricius, 1777) , M. rotundatum , and M. maculatum . Larvae of M. rotundatum and M. linearis have five to six setae on labial palp ( Sahlén & Hedström 2005; De Marmels 2007), M. ornata six ( Ramírez 1995) and M. asticta two ( Lencioni 2006). The larva of M. maculatum , with four or five setae, can be distinguished from those of M. linearis and M. rotundatum as well as from the other pseudostigmatid larvae ( Figs. 12–16 ) by the shape of the gills ( Figs. 13 and 16 , respectively). However, additional specimens will be necessary to further increase our knowledge of M. maculatum and M. rotundatum , since the larvae of these two species were described based on few specimens with damaged gills. There is a high possibility that the three species of Microstigma may represent geographical variants of a single widely distributed species must be taken into account when comparing the larva described here with the others associated with Microstigma .

According to our study and the literature, larvae of all the Mecistogater and Microstigma found in Brazil share the same type of habitats (tree trunk holes) as breeding sites ( Ramírez 1995; Sahlén & Hedström 2005; De Marmels 2007), except M. asticta which is so far only known to develop only within bamboo internodes ( Lencioni 2006) and M. maculatum which also can use bracts of fallen palms in the forest ( Mesquita 1992).

Figures

FIGURE 11. Labial palp of Microstigma maculatum larvae, the blue arrows indicates setae and the red triangle the insertion of fifth setae.

FIGURES 3 – 10. Microstigma maculatum (male): 3) right mandible, dorsal view; 4) right mandible, ventral view; 5) right mandible, apical view; 6) right maxillae; 7) right labial palp; 8) prementum, ventral view, 9) prementum, dorsal view; 10) abdominal segments IX – X, ventral view, male gonapophyses. (Scale Bar: 1 mm).

FIGURES 12 – 16. Larval gills of all known species of Pseudostigmatidae known from Brazil: 12) Microstigma maculatum, right lateral gill; 13) Mecistogaster linearis, median gill (original by Sahlén & Hedström 2005, not to scale); 14) Mecistogaster asticta, lateral gill (original by Lencioni 2006); 15) Mecistogaster ornata (original by Ramírez 1995); 16) Microstigma rotundatum, tip of abdomen showing right lateral and median gills (original by De Marmels 2007, gills of larva damaged). (Scale Bar: 1 mm).