Morphometric analysis of black fly larvae (Diptera: Simuliidae) in Tijuca National Park, Rio de Janeiro, Brazil: A potential tool for biomonitoring aquatic environments

Simulids are dipteran insects that colonize freshwater environments in their immature life stages. This study aims to compare the body size of Simulid larvae of the species Simulium pertinax and Simulium (Inaequalium) sp. collected in waterways inside and outside of Tijuca National Park. Collections were made in 2019 and 2021. Abiotic variables were verified in situ using specific equipment, and a protocol was also applied to assess the integrity of the river waters in each river. A total of 1,311 larvae were collected and found to be the following species: S imulium pertinax, Simulium (Inaequalium) sp., Simulium (Psaroniocompsa) sp., Simulium (Psaroniocompsa) anamariae, and Simulium (Psilopelmia) perflavum . The average body, head, and protorax leg sizes of the larvae were larger in the outer section of the Tijuca River than in the inner section. The Wilcoxon test found a significant difference (p-value < 0.05) in the body size of S. pertinax and S. (Inaequalium) sp. compared to 2019 and 2021. The CCA also showed that the body, head, and propata sizes of S. pertinax were influenced by river brightness and altitude. The correlations between the abiotic variables and morphometric measurements were highly significant. As there are still few studies linking the morphometry of blackfly larvae to river water integrity, this work stands out for advancing in this field. Our results reinforce the potential of these organisms as biological indicators and point to new pathways for the biomonitoring of aquatic environments.