Latias mayfly (Isonychia latias) from Guizhou, China, shows several characters uncommon in the genus

NEWS - Latias mayfly (Isonychia latias sp. nov.) from Guizhou Province, southwest China, was established as a new species to science based on all developmental stages with adults showing some characters that are uncommon in Isonychia, such as brown middle and hind legs, and pale stripes on the thorax.

Isonychiidae is a monogeneric mayfly family represented by the genus Isonychia Eaton 1871 that includes 16 species distributed in the Nearctic region and 21 species distributed in the Palaearctic and Oriental regions.

Recently, researchers conducted a preliminary investigation of the mayfly fauna in Guizhou Province, southwest China, and found an undescribed specimen. This species shows some characters that are uncommon in the genus.

Isonychia latias is named Latias after the red-and-white-winged Pokémon. The larvae have so far only been found in the Sanchahe River in Guizhou Province. The collection site was near the Danxia landform characterized by a large number of dark red rocks in the river.

Larvae are mainly collected in several pieces in fast water currents and single emerging adults are found in shallow gravel areas. Larval exuviae are mainly found on rocks 10-20 cm above the water surface with the highest being more than 50 cm. Subimago of both sexes molt into adults and spend three nights after being captured.

I. latias can be easily distinguished from its relatives by a combination of characters. The male has wings with a distinct dark brown color: on the forewings it occupies a large area of the apical half as a transverse band, a small area around the branching point of Rs, and a margin along the basitornal and tornus edges, and on the hindwings it occupies almost the entire apical half.

The middle and hind legs are brown, almost consistent with the forefemur; the pterothoracic pleura with three yellowish lines formed by pale conjunctiva.

Larva with all-excavated lamellae without spines on the apical edge and without any obvious dots or markings. Abdominal terga I–VII with pale median longitudinal stripes, terga II–IX with a pair of pale submedian longitudinal stripes, and tergum X with a pair of light spots near the anterior margin. Caudalii are brown basally and gradually paler towards the apex without a dark band medially.

I. latias larvae resemble I. fuscimarginata larvae Qiang et al., 2024. However, each tergal lamella has a large dark purple spot in the center at the base in I. fuscimarginata (vs. no spot in I. latias). Ventral fibrillar lobes of tergal with fewer filaments (vs. more numerous). Submedian dark band on all caudalii and apical dark band on cerci (vs. no dark band along the body).

The researchers performed a multi-gene phylogenetic analysis using mitochondrial COI and 16S genes on the new species, 4 Isonychia s.s. species, and 1 Prionoides species. Chromarcys magnifica Navás 1932 and Paegniodes cupulatus (Eaton, 1871) were used as outgroups.

The ML tree topology shows Isonychia (Prionoides) shima (Matsumura, 1931) as the first species to branch, forming a sister group to the remaining species. Within the remaining species, the new species was the first to split, forming a sister group to the other four Isonychia s.s. species, forming a monophyletic group.

Original research

Mu P, Huang X (2024). Discovery of a new Isonychia species with distinctive characters from southwestern China, and preliminary exploration of its phylogenetic status (Ephemeroptera, Isonychiidae). ZooKeys 1218: 135-151, DOI:10.3897/zookeys.1218.137110

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