Microstigma maculatum Hagen

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).