Taxonomic notes on Crocothemis erythraea (Brullé, 1832) (Odonata: Libellulidae) from the Western Ghats of Peninsular India

The genus Crocothemis Brauer, 1868 (Odonata: Libellulidae) has two species distributed in the Indian region: Crocothemis erythraea (Brullé, 1832) and C. servilia (Drury, 1773). Crocothemis servilia is a common species in the lowlands of southern India, whereas C. erythraea appears to be a rare species restricted to the higher elevations of the southern Western Ghats. The differentiation of these closely similar species is somewhat problematic in the field, with some authors stating that only C. servilia is present in southern India. We provide taxonomic characteristics that are useful for diagnosing these altitudinally separated species based on their male genitalia. Molecular analysis based on the mitochondrial COI gene recovered high-elevation samples from the Western Ghats within the C. erythraea clade. Furthermore, samples from the lower elevations of the Himalayas and Western Ghats were retrieved within the C. servilia clade, confirming the presence of both species in the Western Ghats. Phylogenetic analysis of C. erythraea populations from the Western Ghats and Himalayas revealed high genetic similarity, with 99.5% identity in COI and ~98.95% identity in ITS2 sequences. This confirms that the taxon represented in the montane regions of the Western Ghats is C. erythraea, whereas the lowland taxon is C. servilia. Important morphological features for comparison of mature insects, field behavior, and the updated distribution of the two species in India are also discussed. The isolation of C. erythraea in the subtropical and temperate montane forests of the Southern Western Ghats, despite its phylogenetic similarity to Himalayan populations, suggests that a relict distribution was likely shaped during the Pleistocene glaciations.