The alderfly genus Indosialis Lestage, 1927 (Megaloptera: Sialidae) in Thailand and Laos, with a description of a new species Author Piraonapicha, Kanyakorn Department of Biology, Faculty of Science, Khon Kaen University, Khon Kaen, 40002, Thailand. Author Sangpradub, Narumon Author Jaitrong, Weeyawat Thailand Natural History Museum, National Science Museum, Technopolis, Khlong 5, Khlong Luang, Pathum Thani, 12120, Thailand. polyrhachis @ yahoo. com; https: // orcid. org / 0000 - 0003 - 1362 - 0754 Author Liu, Xingyue Department of Entomology, China Agricultural University, Beijing 100193, China. text Zootaxa 2020 2020-06-02 4786 2 233 253 journal article 10.11646/zootaxa.4786.2.5 1175-5326 3874723 C1C5F922-7D01-44E2-8AA3-F5BBC4EDFC2C Indosialis siamensis sp. nov. ( Figs. 10–15 ) Type material. Holotype , male, northeastern Thailand , Huai Lek Stream , Wang Saphung District , Loei Province , 17°21’9.76”N , 101°39’23.78’’E , 336 m a.s.l. , 30.III.2020 , K. Piraonapicha leg., THNHM-I-16801 ( THNHM , Pinned specimen) . Paratypes . Three males (THNHM-I-16802 to THNHM-I-16804, THNHM ), 1 female (THNHM- I-16805, THNHM ), same locality and collector as holotype , 13. V .2019; 1 female (THNHM-I-16806, THNHM ), same locality and collector as holotype , 28. V .2019; 1 male (KKUM-001, KKU ) and 2 females (KKUM-002 to KKUM-003, KKU ), same locality and collector as holotype , 30. VI .2019; 1 male (KKUM-004, KKU ), same locality and collector as holotype , 14.II.2020 . The paratypes are preserved in absolute ethanol. Diagnosis. Head and prothorax brown in both sexes. Male. Inner margin of left mandible without small setae; inner margin of right mandible with distinct apical tooth followed by long and sharp preapical tooth and broad basal tooth; gonocoxite 9 in lateral view broadly rounded, with apex slightly narrowed and curved dorsad; ectoproct in lateral view subtriangular, with convex apex. FIGURE 10. Indosialis siamensis sp. nov. (Holotype, THNHM-I-16801), male, A, B. dorsal view; C. lateral view. Scale bars: 5.00 mm. FIGURE 11. Indosialis siamensis sp. nov. (paratype), female in lateral view. Scale bar: 5.00 mm. FIGURE 12. Indosialis siamensis sp. nov. , dorsal view. A. left mandible of male; B. right mandible of male; C. right mandible of female. Scale bar: 0.20 mm. Description. Male ( holotype and paratypes , Figs. 10 , 12 , 13 , 15 ). Body length 7.5 mm ; right forewing length 7.0 mm; right forewing width 2.5 mm , right hind wing length 6.5 mm ; right hind wing width 2.5 mm . Head brown, subquadrate, almost as long as broad; dorsum of head with dense brownish irregular raised scars on posterior half; labrum brown, elliptical, clearly shorter than broad, anterior margin weakly concave, and covered with dense long erect setae; mandibles asymmetrical, smooth and shiny; left mandible with long and blunt apical tooth, followed by broad preapical tooth and small triangular basal tooth; basal margin of left mandible feebly concave; without setae on inner margin of mandible; outer margin of left mandible feebly convex ( Fig. 12A ); right mandible with distinct (small and sharp) apical tooth, followed by large, long and sharp preapical tooth and broad basal tooth on inner margin; outer margin of right mandible convex ( Fig. 12B ); clypeus yellowish brown, relatively short, and its anterior margin concave medially; compound eye dark, relatively large and roundly convex, located anterior to mid-length of head; scape and pedicel yellowish brown, scape almost twice as long as pedicel, flagellum dark brown. Thorax brown; pronotum (excluding anterior and posterior membranes) in dorsal view, subrectangular, clearly shorter than broad, with almost parallel lateral margins; setae on pronotum brown; mesonotum in dorsal view, subrectangular, almost as long as metanotum. Wings grayish brown; veins brown; forewing about 2.80 times as long as broad; costal region with 6–8 distinct cross-veins; hindwing slightly shorter than forewing, about 2.60 times as long as broad; costal region with 3 distinct costal crossveins; wings entirely covered with dense erect long setae mixed with dense short setae. Legs covered with decumbent setae (setae on legs clearly longer than on wings); coxae yellowish brown; femora, tibiae and tarsi brown (tarsi darker than former two), pretarsal claws pale brown. Abdomen brown, abdominal segments 1–8 each with a pair of yellow spots medially. FIGURE 13. Indosialis siamensis sp. nov. , male genitalia (paratype), A . dorsal view; B. ventral view; C. lateral view; D. caudal view. Sac.: sac-like structure. Scale bar: 0.20 mm. Genitalia. Tergum 9 in dorsal view, subtrapezoidal, with its anterior margin weakly convex and posterior margin extensively concave; sternum 9 in ventral view, as long as broad, with anterior margin almost straight and posterior margin extensively convex; gonocoxite 9 in lateral view, broad, ventral margin convex, dorsal margin weakly sinuate with posterodorsal corner slightly produced; ectoproct in lateral view, subtriangular, convex distal and curved inward; fused gonocoxites 11 in lateral view, with narrowed, gonostyli 11 directed posteriorly; in dorsal view, gonostyli 11 present as a pair of relatively stout spines, which are narrowed gradually to apex. Large sac-like structure present in male genitalia ( Fig. 13 ). Female ( paratypes , n = 3, Fig. 11 , 12 , 14 ). Body length 7.5–8.5 mm ; right forewing length 8.5–9.5 mm ; forewing width 2.5–3.0 mm; right hindwing length 7.5–9.0 mm; right hindwing width 3.0– 3.5 mm . Similar to the male in structure, sculpture, color, wing venation and pilosity, with the following condition that should be noted: Body slightly larger; mandibles symmetrical, each with large and blunt apical tooth, followed by medium-sized of blunt tooth and small triangular basal tooth ( Fig. 12C ); sternum 7 broadly pentagonal in ventral view; gonocoxites 8 separated into a pair of subrectangular lobes, partly concealed under sternum 7; gonapophysis 8 subtrapezoidal, clearly shorter than broad, with some setae; gonocoxites 9 present a pair of broad ovoid valves, with small gonostyli 9 at tip; ectoprocts paired, small, and ovoid ( Fig. 14 ). FIGURE 14. Indosialis siamensis sp. nov. , female abdominal apex (paratype), A . ventral view; B. gonapophysis 8, ventral view; C. lateral view. Scale bar: 0.50 mm (A, C); 0.25 mm (B). Etymology. The specific name is an adjective meaning ‘of siam (a historic name of Thailand )’. DNA barcode data. In the maximum likelihood and neighbor-joining analyses, the adult males and females of I. siamensis from Loei Province were genetically distinct from I. bannaensis ( Fig. 16 ), being consistent to the morphological identification. The COI intraspecific divergence ranged from 0 to 0.023, while the interspecific divergence between the two Thai Indosialis species ranged 0.043 to 0.062 (GenBank Accession Numbers: MN087710 – MN0815). Habitat. The adults of I. siamensis were collected by light traps close to a slow-flowing or sluggish stream which is usually covered by C. esculenta (Araceae) . The new species coexists with I. bannaensis in Loei Province . Distribution. Thailand ( Loei ) ( Fig. 17 ). FIGURE 15. Indosialis spp. Indosialis siamensis sp. nov. ( A, C, E, G ); Indosialis bannaensis ( B, D, F, H ). A, B . dorsal view; C, D. ventral view; E, F. lateral view; G, H. caudal view. Scale bar: 0.20 mm (A, C, E, G); 0.50 mm (B, D, F, H). Remarks. The new species can be distinguished from I. bannaensis as well as the other two Indosialis species by the following characteristics: 1) head and pronotum brown (orange in I. bannaensis and other species); 2) apical tooth of right mandible in male sharply produced (obtusely prominent in I. bannaensis ); 3) inner margin of left mandible in male without short setae (with small setae in I. bannaensis ); 4) presence of large sac-like structure in male genitalia (indistinct or absent in I. bannaensis and other species); 5) male gonocoxite 9 in lateral view with posterodorsal corner slightly produced (male gonocoxite 9 in lateral view with apex distinctly narrowed and curved dorsad in I. bannaensis ); 6) male gonostyli 11 relatively stout (much more slender in I. bannaensis ); 7) male ectoprocts not distinctly narrowed distad and incurved (male ectoprocts distinctly narrowed distad and incurved in I. bannaensis and other species) ( Fig. 15 ).