Rheocricotopus (Psilocricotopus) sirventorum Andersen & Mendes, 2012

Pinho, Luiz Carlos & Andersen, Trond, 2023, The immature stages and female imago of Rheocricotopus (Psilocricotopus) sirventorum Andersen & Mendes, 2012, a Neotropical member of the chalybeatus species group (Diptera, Chironomidae, Orthocladiinae), Zootaxa 5375 (4), pp. 595-600 : 596-598

Rheocricotopus (Psilocricotopus) sirventorum Andersen & Mendes, 2012

( Figs 1 – 9 )

Material examined. 5 males and 1 female with pupal and larval exuviae, slide-mounted: BRAZIL, Santa Catarina State, Santo Amaro da Imperatriz, Colônia Santa Luzia (Pagará), S27°38’31” W48°45’17”, 08.xii.2015, hand net, LC Pinho et al. ( CE-MHS) .

Description

Adult female (n = 1). Total length 1.60 mm. Wing length 1.03 mm. Total length / wing length 1.55. Wing length / length of profemur 2.43.

Coloration. Head light brown, palp brown. Thorax light brown with brown pigmentation in posterior area of scutum, postpronotum, postnotum, epimeron II and halter. Legs uniformly light brown. Abdominal tergite I brown, tergites II–VIII light brown with wide (about 0.6 of tergite length) transverse brown bands. Wings unmarked.

Head. Eyes bare, frontal tubercles absent. AR = 0.45; flagellomere lengths (in μm): 55, 30, 37, 40, 72. Temporal setae 5. Clypeus with 15 setae. Tentorium 117 μm long, 12 μm wide. Palpomere lengths (in μm): 32, 37, 62, 97, 149. Third palpomere with 2 sensilla clavata, longest 15 μm.

Wing. VR = 1.08. Brachiolum with 1 seta, R with 6 setae, R 1 with 4, R 4+5 with 6 setae, remaining veins bare. Anal lobe weak. Squama with 8 setae.

Thorax. Antepronotum with 2 setae. Dorsocentrals 40 in 1–4 irregular rows, acrostichals absent, prealars 5, supraalar absent. Scutellum with 8 setae, uniserial.

Legs. Spur of fore tibia 27 μm long, spurs of mid tibia 37 μm and 20 μm long, spurs of hind tibia 35 μm and 30 μm long. Width at apex of fore tibia 29 μm, of mid tibia 29 μm, of hind tibia 44 μm. Comb with 8 setae, longest 30 μm, shortest 25 μm long. Tarsomere 1 of mid leg with 5 sensilla chaetica in basal one-third. Length and proportions of legs as in Table 1 .

Genitalia ( Figs 1, 2 ). Gonocoxite with 2 setae. Tergite IX undivided with 2 setae. Cercus 62 μm long. Seminal capsules excluding neck 85 μm long, 59 μm wide; with 9 μm long neck. Notum 97 μm long.

Pupa (n = 4–6). Total length 2.41–2.75, 2.54 mm. Length of thoracic horn / length of anal macrosetae 0.83– 0.85, 0.84. Exuviae transparent.

Cephalothorax. Frontal setae on prefrons ( Fig. 3 ), 17–27, 23 μm long. Median antepronotals 47–80, 67 μm long, lateral antepronotal 27–55, 40 μm long. Thoracic horn ( Fig. 4 ) 187–219, 207 μm long, 20–35, 27 μm wide. Anterior precorneal seta 55–87, 70 μm long; median 50–87, 65 μm long; posterior 87–125, 107 μm long and stronger. Anterior dorsocentral (Dc 1) 40–60, 50 μm long; Dc 2 25–40, 32 μm long; Dc 3 17–25, 21 μm long; Dc 4 12–45, 31 μm long. Distance between Dc 1 and Dc 2 25–45, 37 μm, between Dc 2 and Dc 3 32–47, 44 μm, between Dc 3 and Dc 4 20–45, 32 μm.

Abdomen ( Fig. 5 ). Tergite I (T I) bare; T II–V nearly bare, with indication of lateral spinules; T VI–VIII with sparse median shagreen; T IX with anterior shagreen. Sternites I (S I) and IX bare, S II–V with sparse anteromedian and lateral shagreen, S VI–VIII with median and lateral shagreen. Pedes spurii A present on S IV–VI. Pedes spurii B absent. T II with 40–59, 50 caudal hooklets. Number of caudal spines on T III–VIII as: 49–79, 66; 56–81, 69; 60–84, 67; 55–82, 65; 33–52, 46; 28–35, 33. Maximum length (in μm) of caudal spines on T III–VIII as: 20–25, 22; 22–27, 25; 22–27, 25; 25–30, 27; 17–22, 20; 14–17, 15. Conjunctives III/IV, IV/V and V/VI with median spinules in multiple rows. L setae on segments I–VIII as: 2, 3, 3, 3, 3, 3, 4, 5. All L setae lamelliform on segments VII and VIII, bristle like on anterior segments. Anal lobe with 25–30, 28 setae in fringe; anal macrosetae 224–261, 244 μm long.

Larva (n = 4–6). Total length not measurable. Head capsule length 333–368, 348 mm.

Head. Antenna as in Fig. 6 . Lengths of antennal segments (in μm): 52–57, 55; 17–22, 20; 4–5, 5; 4–5, 5; 2–3, 3. AR = 1.57–1.92, 1.70. Basal antennal segment 62–65, 64 μm wide, distance from base to ring organ 5 (1) μm. Blade 20–25, 22 μm long, accessory blade 7–10, 9 μm long. Labrum and epipharyngeal area about as in Fig. 7 , with outer scales of pecten epipharyngis broader than median scale. Premandible 60–67, 64 μm long. Mandible ( Fig. 8 ) 97–122, 112 μm long. Mentum as in Fig. 9 , ventromental plate 12–17, 15 μm wide, with about 20 setae underneath. Postmentum 206–211, 208 μm long.

Abdomen. Longest body setae 115 μm (1). Procercus 49–54 (2) μm long, 29–34 (2) μm wide, with median and basal spurs; anal setae 431–441 (2) μm long. Suprananal seta 103–108 (2) μm long. Length of supraanal seta / length of anal seta 0.23–0.24 (2). Posterior parapods 98 (1) μm long. Anal tubules not discernible.

Distribution and biology. The species was described originally from Mato Grosso State in the Amazonian region ( Andersen & Mendes 2012); the range is now extended to the Atlantic Forest in Santa Catarina State, southern Brazil. The larvae were collected attached to marginal aquatic vegetation in a fast-flowing low-order stream.

Figures

FIGURES 1–9. Rheocricotopus (Psilocricotopus) sirventorum Andersen & Mendes, 2012, adult female (1, 2), pupa (3–5) and larva (6–9). 1, genitalia, ventral view; 2, genitalia, dorsal view; 3, frontal apotome and prefrons; 4, thoracic horn and precorneals; 5, abdominal tergites; 6, antenna; 7, labrum and epipharyngeal area; 8, mandible; 9, mentum.