Larval odonate assemblage structure in a disturbed rainforest stream of the southern Western Ghats, Kerala, India

Abstract

Larval odonate assemblages were investigated in the Kallar stream system, a perennial hill stream of the southern Western Ghats in Thiruvananthapuram District, Kerala, India. Monthly sampling was conducted at five sites (Darpha-Kalungu, Pottanchira, Kaliyikkal, Meenmutty and Main Kallar) that differed in riparian cover, land use and substrate composition. Larvae were collected from multiple microhabitats including sand, gravel, cobble, boulder and leaf-litter deposits using hand nets and direct substrate examination and were identified using standard taxonomic keys. A total of 3,090 individuals belonging to 12 families and 39 morphospecies were recorded. Dragonfly larvae dominated the assemblage, with Gomphidae showing the highest abundance. Open-canopy sites associated with settlements and plantations were mainly represented by widespread families such as Libellulidae and Gomphidae, whereas shaded forest reaches containing leaf litter and woody debris supported additional families including Platystictidae, Protoneuridae and Euphaeidae. Damselflies were more frequent in shaded stretches, while sandy reaches supported fewer individuals. The results indicate that riparian canopy cover and substrate heterogeneity strongly influence odonate larval distribution and emphasize the importance of maintaining natural riparian vegetation in Western Ghats hill streams.