Cloeon bicolor Kimmins, 1947

Noenrimnong, Chayanon, Suttinun, Chanaporn, Tungpairojwong, Nisarat & Boonsoong, Boonsatien, 2026, Taxonomic insights into the diversity of Cloeon Leach, 1815 (Ephemeroptera, Baetidae) in Thailand, ZooKeys 1266, pp. 1-39 : 1-39

Cloeon bicolor Kimmins, 1947

Figs 2 A – C , 7 C , 8 C, D , 10 C, D , 13 C, D , 15 C, D , 21 A – D , 27 D , 28 C , 29 C

Cloeon bicolor Kimmins, 1947: 97, figs 4, 8, 12 (original description, male and female).

Cloeon bicolor Kimmins: Gillies 1949: 173. Kimmins 1971: 311 (list). Hubbard and Peters 1978: 8. Hubbard and Srivastava 1984: 3. Selvakumar et al. 2016: 653 (data on DNA). Kubendran et al. 2017: 615. Ying et al. 2021: 2, figs 1 A, B, 2, 3 A, 3 E, 3 I, 3 M, 4, 5 A, B, 6 A, B, 7 A – C, 8 A, B (nymph first description). Kluge 2022: 161, 166. Kubendran et al. 2022: 398, figs 1–17 (record).

Material examined.

• 1 nymph, 1 female imago, Bangkok Prov., Luang Suwannawajokkasikij 100 th Year Park , 13°50'54.5"N, 100°34'15.1"E, 1. VIII. 2024, C. Noenrimnong leg. ( ZMKU) ; • 1 female subimago, 2 male imagos, Bangkok Prov., Charn at the Avenue , 13°53'40.8"N, 100°33'27.8"E, 26. XI. 2024, S. Kwanboon leg. ( ZMKU) ; • 1 male subimago, 1 female subimago, Lop Buri Prov., Huai Som , 14°51'52.3"N, 100°51'28.1"E, 19. I. 2025, A. Wongyam leg. ( ZMKU) ; • 2 female imagos, Chanthaburi Prov., Laemsing , 12°29'05.0"N, 102°04'10.2"E, 29. XII. 2024, C. Noenrimnong leg. ( ZMKU) ; • 1 male imago, Nakhon Ratchasima Prov., Non Sung , 15°14'05.5"N, 102°22'40.6"E, 19. V. 2025, B. Boonsoong leg. ( ZMKU) ; • 1 nymph, Nakhon Ratchasima Prov., Motorway M 6 , 14°53'09.8"N, 101°37'17.5"E, 19. V. 2025, B. Boonsoong leg. ( ZMKU) ; • 1 female imago, Buri Ram Prov., Mafueang Phutthaisong , 15°29'54.0"N, 103°02'58.2"E, 16. V. 2025, B. Boonsoong leg. ( ZMKU) ; • 2 nymphs, Khon Kaen Prov., Sithan Lake KKU , 16°26'41.1"N, 102°48'55.0"E, 1. IV. 2024, N. Tungpairojwong leg. ( KKU) ; • 7 nymphs, Khon Kaen Prov., Fisheries Pond KKU , 16°27'31.5"N, 102°48'38.3"E, 1. IV. 2024, N. Tungpairojwong leg. ( KKU) ; • 4 male imagos, Roi Et Prov., Na Pho Subdistrict , 15°57'48.8"N, 103°34'08.2"E, 10. VII. 2025, W. Singsanan leg. ( ZMKU) ; • 4 nymphs, 1 female subimago, Ubon Ratchathani Prov., Ubon Ratchathani University , 15°07'06.1"N, 104°54'09.4"E, 22. VIII. 2025, B. Boonsoong leg. ( ZMKU) ; • 1 female imago, Bangkok Prov., Chalermprakiat 55 th Year Park , 13°51'17.0"N, 100°34'27.7"E, 1. VIII. 2024, C. Noenrimnong leg. ( ZMKU) ; • 1 male imago, Nakhon Pathom Prov., Chawalun Resort , 13°56'31.7"N, 100°03'12.7"E, 13. I. 2025, S. Kwanboon leg. ( ZMKU) ; • 3 female imagos, Chachoengsao Prov., Sao Cha-Ngok , 13°41'43.1"N, 101°09'13.5"E, 8. XI. 2024, B. Boonsoong leg. ( ZMKU) .

Description

(in alcohol). Female imago. See Kimmins (1947) for original description.

The female imagos are characterised by a yellow head, with a pale-yellow midline flanked by two dark brown longitudinal stripes across the central region (Fig. 21 A ). The thorax is yellow, with a yellow midline bordered by two narrow, long, pale brown longitudinal stripes extending from the head (Fig. 21 A ). The abdominal terga are yellow, with uniformly brown to dark reddish-brown pigmentation. Terga II – IX have a pale midline flanked by a pair of pale spots or drop-shaped markings, while the lateral margins of each anterior segment bear dark reddish-brown spots or stripes (Fig. 13 C ). The abdominal sterna display dark reddish-brown stripes along the lateral margins of segments II – VIII (Fig. 15 C ). The wings are hyaline, with a pale-yellow stripe in the costal area and a dark brown stripe in the subcostal area (Fig. 10 C ).

Male imago (Fig. 7 C ). See Kimmins (1947) for original description. The male imagos of this species can be identified by their hyaline wings (Fig. 10 D ), which lack strong pigmentation except for a pale-yellow stripe in the costal area and a dark brown stripe in the subcostal area. The abdominal terga are translucent white, with segments II – VII showing similar patterns to those of the female but narrower, featuring faint reddish-brown spots along the lateral margins. Terga VIII – X are orange to dark orange in colouration (Fig. 13 D ). The abdominal sterna of segments VIII – X are white and unpigmented (Figs 13 D , 15 D , 21 B ). The compound eyes are orange to orange-yellow, with olive-green lower portions (Fig. 8 D ).

Nymph. See Ying et al. (2021) for first description. The mature nymphs possess a head with two rows of irregular brown spots (Fig. 2 A ). The abdominal terga are dark green to brown, with uniformly dark brown to reddish-brown colouration. Terga II – IX bear a pale midline flanked by a pair of pale spots or drop-shaped marks. Segments II and V may appear darker, with interruptions in the midline, while segments IV and VII are comparatively paler (Fig. 2 A, B ). The abdominal sternum X lacks dark pigmentation (Fig. 2 C ).

Egg. Width 71.61 μm; height 95.98 μm; granules ranging from 0.086 –0.118 μm. Oval to nearly round; surface covered with granules of similar size, distributed unevenly. Some areas of surface appear smoother, with more widely spaced granules (Fig. 21 C, D ).

Distribution.

Northeastern Thailand ( Buri Ram, Khon Kaen, Nakhon Ratchasima, Roi Et, and Ubon Ratchathani provinces); central Thailand ( Bangkok, Lop Buri, and Nakhon Pathom provinces); eastern Thailand ( Chachoengsao and Chanthaburi provinces).

Remarks.

The adults of Cloeon bicolor were described by Kimmins (1947) based on materials from Bengal ( India). This species was also recorded from China and the nymph was described by Ying et al. (2021). In this study, we provide the first description of the egg structure of C. bicolor .

Figures

Figure 2. Cloeon bicolor, mature nymph morphology: A. Male mature nymph (dorsal view); B. Terga I – X; C. Sterna I – X.

Figure 7. Live habitus of imago of Cloeon species in Thailand: A. Female of Cloeon rubellum; B. Male of Cloeon rubellum; C. Male of Cloeon bicolor; D. Female of Cloeon viridulum.

Figure 8. Adult habitus of Cloeon species in Thailand: A. Female of Cloeon bengalense; B. Male of Cloeon bengalense; C. Female of Cloeon bicolor; D. Male of Cloeon bicolor.

Figure 10. Wings of Cloeon species in Thailand: A. Female of Cloeon bengalense; B. Male of Cloeon bengalense; C. Female of Cloeon bicolor; D. Male of Cloeon bicolor.

Figure 13. Adult abdominal terga of Cloeon species in Thailand: A. Female of Cloeon bengalense; B. Male of Cloeon bengalense; C. Female of Cloeon bicolor; D. Male of Cloeon bicolor.

Figure 15. Adult abdominal sterna of Cloeon species in Thailand: A. Female of Cloeon bengalense; B. Male of Cloeon bengalense; C. Female of Cloeon bicolor; D. Male of Cloeon bicolor.

Figure 21. Cloeon bicolor, Adult morphology: A. Head and thorax of female imago (dorsal view); B. Sterna VIII – X of male imago (ventral view), SEMs of egg structures: C. General outline of egg; D. Chorion surface.

Figure 27. Drawing showing the dorsal (left) and ventral (right) views of a mature nymph Cloeon species in Thailand: A. Cloeon harveyi; B. Cloeon rubellum; C. Cloeon bengalense; D. Cloeon bicolor; E. Cloeon viridulum.

Figure 28. Drawing showing the dorsal (left) and ventral (right) views of a female imago of Cloeon species in Thailand: A. Cloeon rubellum; B. Cloeon harveyi; C. Cloeon bicolor; D. Cloeon viridulum; E. Cloeon bengalense.

Figure 29. Drawing showing the dorsal (left) and ventral (right) views of a male adult of Cloeon species in Thailand: A. Cloeon harveyi (imago); B. Cloeon viridulum (subimago); C. Cloeon bicolor (imago); D. Cloeon bengalense (imago); E. Cloeon rubellum (imago).