The male adult of Molanna truncata Ge, Peng & Sun sp. nov. is described and illustrated based on material collected in Si-chuan, China. It could be diagnosed by the subtriangular superior appendages when viewed dorsally, and by the mesal appendages each having a slender thorn and inferior appendages with a tiny inner process. Based on morphology of genitalia, we provide a dichotomous key to adult males of Molanna from the Oriental region. The DNA barcodes (partial mt COI sequences) of M. truncata sp. nov. are generated and compared with existing sequences of Molanna species from Oriental and Palearctic regions. The mean intraspecific divergence of Molanna was 1.58% with a maximum of 8.50% in M. moesta. The Automatic Barcode Gap Discovery (ABGD) analysis of Molanna inferred 9 OTUs and thresholds of interspecific divergence of 10%. Divergence of M. truncata sp. nov. haplotypes from all other Molanna haplotypes ranged from 10.1% to 18%. We discuss distribution and potential groups of species within the Oriental Molanna species based on morphology.

Caddisflies, COI sequence, integrative taxonomy, morphology, Oriental region, wing venation

Molannidae Wallengren, 1891 is a small family of Holarctic and Oriental biogeographic regions, with two genera, Molanna Curtis, 1834 and Molannodes McLachlan, 1866 (Morse 2021). Curtis (1834) erected the genus Molanna with Molanna angustata Curtis, 1834 as the type species by original designation. At present, the genus includes 25 extant species and three fossil species worldwide (Morse 2021). Among them, 12 species were reported from the Oriental region, six were restricted to the Nearctic region, four from the Palaearctic region and two from the East Palaearctic region; only M. moesta Banks, 1906 occurs in both the East Palaearctic and Oriental regions (Banks 1906; Malicky and Chantaramongkol 1989; Nebois 1993; Malicky 1994; Ito 2006). At present, three species were reported from China, among them, M. moesta, distributed from northeast to southwest in China (i.e. Hei-long-jiang, Jiang-xi, Guang-dong, Si-chuan, Gui-zhou and Yun-nan), while M. kunmingensis Hwang, 1957 and M. xiaguana Malicky, 1994 are reported from the Yunnan Province exclusively (Yang et al. 2016).

Adults of Molanna live around lakes or running waters and are easy to recognize because in repose the adults look like short branch segments (Schmid 1998). Larvae mostly occur in lakes or slower currents of streams, and inhabit sandy substrates (Wiggins 1996). Larvae of Molanna flavicornis Banks, 1914 were found to inhabit the profundal zone (up to 20 m deep; Neave 1933).

DNA barcodes, the 658 bp fragment of the mitochondrial gene cytochrome c oxidase I unit (COI), has provided important evidence to confirm new species and has proved to be useful for association between larvae and adults (Hebert et al. 2003; Zhou et al. 2007; Xu et al. 2018; Hu et al. 2019; Ge et al. 2020). But existing DNA barcodes of Molanna species from China are very few, and only one barcode has, to date, been recorded in Barcode of Life Data Systems (BOLD) (Ratnasingham and Hebert 2013). This lack of barcode resources greatly restricts accurate monitoring of Molanna species for metabarcoding of environmental DNA (Lin et al. 2021).

In this study, we describe a new Chinese species of Molanna and provide DNA barcodes of this species. The variation in male hind wing venation and DNA barcodes among species from the Palaearctic and Oriental regions are discussed. Finally, a key and map with distribution to the known adults of Molanna from the Oriental region are given.

In order to verify the description of Molanna truncata sp. nov., we compared the illustrations of male genitalia of all available species and wing venations of most species (Curtis 1834; Banks 1906; Hwang 1957; Wiggins 1968; Malicky and Chantaramongkol 1989; Nebois 1993; Malicky 1994; Ito 1998, 2006; Oláh and Johanson 2010). The male genitalia varied greatly among Molanna species in the superior appendages, the mesal appendages and in the inferior appendages. However, some species showed similarities in these characters, as well as in the hindwing venation. Considering the above-mentioned similarities and differences in morphology, we could argue for particular groups of species within the Oriental Molanna species.

The first group is characterised by the superior appendages with the height at least twice as long as its length or approximately equal to its length, and the media veins unbranched or occasionally 2-branched in hindwings. This group could be further divided into three subgroups according to morphology of the mesal appendages, inferior appendages and venation degeneration in the hindwings. The first subgroup consists of M. paramoesta Wiggins, 1968 and M. moesta, in which the posterior margins of the superior appendages are concave, the mesal appendages are oblique and unfurcated at the distal end when viewed laterally; and the inferior appendages are without any ventral processes. Although these two species both have a wide distribution in the Oriental region, but their ranges do not overlap. The second subgroup consists of M. gamdaha Oláh & Johanson, 2010, M. crinita Wiggins, 1968, M. saetigera Wiggins, 1968 and M. oglamar Malicky & Chantaramongkol, 1989. In this subgroup, the mesal appendages are furcated at the distal end, the inferior appendages divided into dorsal, ventral and inner processes. Furthermore, media veins are usually unbranched and fused with cubitus at the base or at the distal end. Unlike M. paramoesta and M. moesta, these four species are regional endemics, also with non-overlapping ranges. The relatively localized dispersal of adults and the disjunct distribution of adequate habitats in some cases lead to small scale allopatric speciation (Vitecek et al. 2015; Thomas et al. 2020). Molanna saetigera and M. paramoesta, on the contrary, have overlapping ranges. The third subgroup is composed of M. truncata sp. nov. and M. yaeyamensis in which the mesal appendages are unfurcated at the distal end in lateral view. The inferior appendages and media veins are, however, the same as in the latter group.

The second group is characterised by the digitate superior appendages and the variable mesal appendages, which are either hammer-like or with their distal ends curved ventrad. The hindwings have relatively complete venation. We divided the group into two subgroups based on the shape of inferior appendages. The first subgroup consists of M. taprobane Flint, 1973 and M. xiaguana, having elongate-triangular inferior appendages. The second subgroup consists of M. jolandae Neboiss, 1993 and M. cupripennis Ulmer, 1906, with bifurcated inferior appendages. both of which show rather unique distribution patterns in Indonesia (i.e., restricted allopatric distribution on Sulawesi; Fig. 3). They exhibit similar morphology, however, genetic data were not available for the current study, thus their relationship and evolutionary history remain to be investigated. Sulawesi island is however, known as a biodiversity hotspot due to its complex geological history (e.g., Tänzler et al. 2016).

Wings are one of the most important organs of insects, and venation modifications may reflect successful adaptation to different environmental conditions. Based on Schmid’s terminology (Schmid 1998) for the hindwing venation of male M. flavicornis, we compared the venation of nine known males of Molanna, and found that venation showed a trend of degradation. Molanna flavicornis and M. uniophila Vorhies, 1909 had the most complete venation in the hindwing, i.e., subcosta was free, radius had 4 branches, media had 2 branches, and cubitus 2 branches. The hindwing venation of these two species could represent the primitive form (Fig. 6A, B). Other species showed venation of hindwings more or less reduced (Figs 6C–J, 7A, B). Regarding the evolution of hindwings venation in the genus, further support from molecular data could help clarify the true evolutionary pattern.

Figure 6. 

Male hind wings of eight known Molanna species. A M. flavicornis B M. uniophila C M. moesta D M. taprobane E M. cupripennis F M. saetigera G M. yaeyamensis H M. jolandae I M. nervosa J M. gamdaha. Scale bar: 200 μm.

In previous barcode studies on Trichoptera, thresholds of intraspecific divergence (as uncorrected pairwise differences in the COI region) have been estimated to reach at most 11.7% in Hydropsychidae Curtis, 1835 (Zhou et al. 2007) and 11% in Drusus Stephens, 1837 (Kučinić et al. 2016). In this study, the ABGD analysis of Molanna inferred 9 OTUs and thresholds of interspecific divergence of 10%; however, it seems that M. moesta has diverged into three geographic populations (M. moesta from Laos, Russia and Japan were recognized as two OTUs; Table 1), with a threshold of intraspecific divergence ranging between 0.30%–8.50% (Table 1). Molanna truncata sp. nov. is morphologically most similar to M. yaeyamensis, but molecular data for the latter were not available. The minimum interspecific divergence was 10.10% between M. truncata sp. nov. and M. XZ sp. As the M. XZ_sp. was collected in close proximity to the known range of M. yaeyamensis, it is highly likely that M. XZ_sp. is indeed M. yaeyamensis. However, in order to check this, we would need to examine the specimen in detail. The suggested clustering of Oriental Molanna into groups and subgroups based on the structure of male genitalia and the hindwing venation should be further evaluated using an integrated approach, i.e., more detailed morphological analysis encompassing more specimens, a multigene phylogeny including all Molanna species and detailed species distribution (Johanson et al. 2012; Jiang et al. 2021). Such an approach would enable reconstruction of the history of the genus in the Oriental region; however, at present, data are not available.

Figure 7. 

Male hind wings of Molanna truncata sp. nov. and M. crinita. A M. truncata sp. nov. B M. crinita. Scale bar: 200 μm.

Molanna truncata sp. nov. is endemic to Jiuzhaigou Natural Reserve. Apart from this species, we have collected an additional 24 species of Trichoptera (belonging to 22 genera and 14 families) during 2014–2019 in the Reserve (Cao et al. 2016), however, it is the only Molanna species occurring in the area. The area harbours high diversity of freshwater habitats (114 alpine lakes, 17 groups of waterfalls, 47 springs, and 11 sections of rapids; Deng 2012), thus, high diversity of Trichoptera can be expected. The Reserve is an example of typical karst geology, with a high amount of travertine calcite deposits in freshwater habitats (Wang et al. 2018). The majority of the lakes are oligotrophic, with low concentrations of total suspended solids and low turbidity (Li et al. 2020). Water temperature is relatively low in the lakes, whereas conductivity, alkalinity, and pH are relatively high (Cao et al. 2016). Adults of M. truncata sp. nov. were collected from one of such alpine lakes located at altitudes ranging from 2299 to 2377 m.

We are grateful to the editor and the two anonymous reviewers for useful recommendations to improve the manuscript. We are also thankful to Dr Gui-ping Deng from Jiuzhaigou Administration Bureau, for his long-term help and support in our research on aquatic insects of Jiuzhaigou National Nature Reserve during his lifetime. We also want to show appreciation to Ms Yu Wang for helping collect the specimens. This research was supported by the National Natural Science Foundation of China (NSFC, No. 41771052) and the Postgraduate Research & Practice Innovation Program of Jiangsu Province (No. KYCX20_0595).