A laboratory system for rearing Simuliidae (Diptera) under simulated lotic environments.

BACKGROUND: Black flies (Diptera: Simuliidae) are ecologically important components of lotic ecosystems and a public health concern due to their aggressive biting behavior, pathogen transmission, and induction of allergic and inflammatory reactions in humans and livestock. Despite their relevance, experimental research on Simuliidae remains limited compared with other dipteran vectors, largely because their immature stages require specific aquatic conditions that are difficult to reproduce in the laboratory. Larval development depends on continuous water flow, high dissolved oxygen, and suspended particulate food, factors that have hindered the establishment of reproducible rearing protocols. Here, we assess the feasibility and efficiency of rearing Simuliidae through their aquatic stages under controlled laboratory conditions approximating natural lotic environments.

METHODS: Egg masses were collected from submerged substrates in the São Pedro River (Macaé, Rio de Janeiro, Brazil) and transported to the Institute of Biodiversity and Sustainability (NUPEM/UFRJ) aquatic bioterium. Eggs were incubated in aerated containers until hatching, and larvae were transferred to a circular rearing system generating continuous unidirectional flow using submersible pumps. Physicochemical parameters were monitored daily (20-25 °C; pH 7.0; ammonia and nitrite ≤ 0.25 ppm). Larvae were fed a standardized suspension of yeast, spirulina, and chlorella. Eleven independent experiments monitored development from hatching to pupation. Additional assays tested larval densities (50, 100, 200 individuals) and survival following flow interruption. Pupal viability was assessed through adult emergence.

RESULTS: Mean egg hatching success was 74%. Under continuous flow, larval survival averaged 92%, with pupation occurring within 13-15 days. Adult emergence reached 92.5%, indicating high pupal viability. Increased density caused only modest survival reduction, demonstrating system robustness. In contrast, flow interruption caused rapid mortality after 24 h, confirming strict dependence on oxygenated flow. Morphological identification revealed five species-Simulium pertinax, S. subpallidum, S. nigrimanum, S. hirtipupa, and S. rubritorax -indicating frequent multispecies oviposition.

DISCUSSION: Simuliidae can be reliably reared through aquatic stages under laboratory conditions when hydrodynamic and physicochemical parameters are controlled. Although long-term colonization was not achieved, the protocol provides a reproducible framework for experimental studies on simuliid development, physiology, and biting-associated allergic responses.