Stenochironomus jubatus Borkent

Dantas, Galileu P. S., Hamada, Neusa & Mendes, Humberto F., 2016, Contribution to the knowledge of Stenochironomus Kieffer (Diptera, Chironomidae) from Brazil: seven new species and description of females and immatures of some previously known species, Zootaxa 4117 (1), pp. 1-47 : 25-27

Stenochironomus jubatus Borkent

( Figs. 18–19 )

Material examined. Brazil, Amazonas: Novo Airão, Km 3 do ramal do Hotel Mercuri, 02º 50' 44.4" S, 60º 54' 56.9" W, in decayed wood, G.P.S, Dantas, S.C. Escarpinati ( INPA): 1 male with pupal exuviae, 08.x.2008; 1 female with pupal exuviae, 13.x.2008; 1 pupa with larval exuviae, 03.xi.2008; larval exuviae, 25.x.2008.

Diagnostic characters. Male: lateral vitta with two dark patches, one anterior to the other; anal point large at base and bulbous at apex; inferior volsella with two pre-apical setae, one longer than the other; RM with about 5 setae. Pupae: brown, with frontal warts ball-shaped; pedes spurii B present on S II. Larvae: ventromental plate with weak crests near to anterior margin; SI and SII pinnate, SIII simple; labiohypopharynx with ligular lobes truncated without small projection on lateral margin; micropore located postero-laterally to the setae submenti.

Pupa (n = 1). Total length 9.49 mm. Coloration: cephalothorax and abdomen brown.

Cephalothorax ( Figs. 18 A, 18B). Frontal apotome elongated; frontal warts present, ball-shaped ( Fig. 18 A). Precorneal seta 50 µm long. Dorsocentrals (Dc) 80 µm long. Distance between Dc1 and Dc2 6 µm; between Dc2 and Dc3 352 µm; between Dc3 and Dc4 6 µm. Median suture granulose.

Abdomen ( Figs. 18 C, 18D). T I bare ; T II–III with large field of shagreen; T IV–T V with central field of shagreen, thicker near posterior margin; T VI with an anterior field of fine shagreen and a posterior field of thick shagreen, separated by an area without shagreen; T VII–VIII without shagreen; anal segment with anterior pair of shagreen patches. TII with posterior row of hooklets extending to lateral margin of tergite, divided medially into two groups by a distance of 147 µm. Abdominal setation: S I without L setae; S II–IV with 3 L setae; S V–VII with 4 LS setae; S VIII with 5 LS setae. Pedes spurii B present on segment II ( Fig. 18 C). Spur on S VIII with 5–6 brownish teeth, the largest 72 µm long ( Fig. 18 E). Genital sac 589 µm long, overreaching the posterior margin of the anal lobe by 28 µm; anal lobe 499 µm long, rounded at apex, with fringe of about 100 filaments.

Fourth-instar larva (n = 2 except when otherwise stated). Total length 11.88 (1) mm. Head capsule 977 (1) µm long.

Head. Antenna as in Figure 19 A; lengths of antennal segments (in µm): 117–122; 38–42; 17–19; 18; 6–7. Blade 34–38 µm long. Labral lamella with two groups of spicules arranged comblike, spicules of pecten epipharyngis simple, arranged in a row. S1 pinnate, 40–45 µm long; S2 pinnate, 39–50 µm long; S3 simple, 37–38 µm long. Premandible 127–131 µm long. Mandible ( Fig. 19 B) 334–342 µm long, with 4 inner teeth. Mentum concave ( Fig. 19 D), 208–246 µm wide, apparently with 10 blackish teeth (it may have 12 teeth and the outermost tooth would not be seen, due to the curvature of mentum); micropore located postero-rolateral to setae submenti; ventromental plate with weak crests near anterior margin. Base of dorsolateral strip originating on posterior ⅓ of dorsomedian strip. Labiohypopharynx ( Fig. 19 C) with ligular lobes truncated, with cleft between lobes very narrow, nearly parallel-sided.

Abdomen. Procercus with 8 filaments, associated setae of equal size. Anal papillae with two constrictions; basal portion 415–462 µm long, median portion 475–510 µm long, apical portion 273–320 µm long. The longest anal hook 106 µm long.

Systematic remarks. To divide the genus Stenochironomus in two subgenera, Borkent (1984) includes all the species with leaf-mining larvae in the subgenus S. ( Petalopholeus ). Even without knowing the immature stages of S. jubatus , this species was included in this subgenus and so it was considered leaf-mining. However, with the pupae and larvae described here, there is no doubt that it is a species with wood-mining larvae. The pupa of S. jubatus is similar to S. liviae sp. nov. both have two well-developed frontal warts, being smaller and more rounded in S. jubatus , and larger and triangular in S. liviae sp. nov. Another feature that differentiates the pupae of these two species is the size of the teeth of the spur on T VIII, which are thinner and more elongated in S. jubatus . The larva of S. jubatus is similar to that of S. roquei , being difficult to distinguish them. The small tubercles present on the lateral margin of the labiohypopharynx of S. roquei is absent in S. jubatus and the micropore is located posterolaterally to the setae submenti in the latter species, while in the former it is located anterior-laterally. Although we described the mentum of S. jubatus as have 10 teeth, the real number can be 12. Sometimes due to the curvature of the mentum, the lateralmost teeth are hidden behind the penultimate one.

Notes on biology of the species. The adults were reared from larvae which had been mining wood in a fast flowing, black-water stream, emerging about 40 days after the wood had been collected. The pupae remain with the abdomen partially within the larval exuviae, which in turn keeps its extended form.

Figures

FIGURE 18. Stenochironomus jubatus Borkent, pupa. A, frontal apotome. B, thorax, lateral view. C, tergites I – V. D, tergites VI – IX. E – F, spur on S VIII.

FIGURE 19. Stenochironomus jubatus Borkent, larva. A, antenna. B, mandible. B, mandible. C, Labiohypopharynx. D, mentum and ventromental-plate.