# Integrative Description and Redescription of Black Fly (Diptera: Simuliidae) Species in the Simulium (Gomphostilbia) ceylonicum Species-Group from Thailand

## TL;DR

This study clarifies the taxonomy of black flies in Thailand using both DNA and physical traits, revealing a new species and confirming the identity of another.

## Contribution

The study introduces a new black fly species and provides a comprehensive redescription of an existing one using an integrative taxonomic approach.

## Key findings

- A new black fly species, S. sipoense, was formally described from southern Thailand.
- S. trangense was fully redescribed using specimens from its type locality in Thailand.
- Morphological and molecular evidence confirmed that S. sipoense is conspecific with S. trangense from Malaysia.

## Abstract

The morphological similarity among black flies often leads to misidentification, particularly among closely related species. By using an integrative taxonomic approach, the species status of black flies can be clarified, and sometimes resulting in the discovery of new species. So far, the COI DNA barcoding has revealed several cryptic species within two nominal species, Simulium trangense and S. sheilae, of the S. ceylonicum species-group. Through combining detailed morphological examination of all life stage above the egg with DNA analysis, we successfully redescribed S. trangense, which was originally described briefly from Thailand and later fully redescribed from Malaysian specimens based solely on morphological characteristics. Furthermore, we fully described a new species, formally named S. sipoense sp. nov. from southern Thailand. The new species is conspecific with the species redescribed as S. trangense from Malaysia, as supported by both morphological and molecular evidence. This study represents an important case in black fly taxonomy, highlighting that both the redescription of valid species and the description of new species should be undertaken with caution, using an integrated approach that combines morphological and molecular data.

Utilizing the COI barcoding approach, cryptic diversity has previously been detected within the morphologically recognized Simulium (Gomphostilbia) trangense Jitklang, Kuvangkadilok, Baimai, Takaoka & Adler, 2008 and S. (G.) sheilae Takaoka & Davies, 1995, of the S. (G.) ceylonicum species-group. Here, an unknown black fly species belonging to the S. ceylonicum species-group from southern Thailand was discovered and described as a new species, S. (G.) sipoense sp. nov. In addition, S. (G.) trangense is herein fully redescribed based on specimens collected from its type locality. Based on an integrative taxonomic approach combining morphological and molecular data, the validity of the newly described S. sipoense sp. nov. and the redescribed S. trangense is confirmed. Comparative morphological characteristics and phylogenetic analysis, inferred from COI sequences, suggest that the new species is conspecific with the species redescribed as S. trangense, using specimens collected from Malaysia, and is morphologically and phylogenetically closely related to S. sheilae, particularly to the specimens from Indonesia. The redescribed S. trangense is genetically highly similar or even identical to the species that was apparently misidentified as S. sheilae from southern and western Thailand, and is morphologically very similar to the new species, from which it is clearly distinguished by the relative length of the female claw tooth, shape of the male ventral plate, and color of the larval body. A detailed information on the morphological characteristics separates the new species, and the redescribed S. trangense from all other known species of the same species-group in Thailand and neighboring countries is provided. Further studies are warranted to clarify the taxonomic status of several cryptic species recognized within the morphologically defined S. trangense and S. sheilae.