Cyromazine on Ecologically Friendly Biodac Carrier as a Larvicidal Agent: Evaluation of Its Efficacy in Mosquito Control of Culex pipiens

Culex pipiens is a widespread mosquito species with high ecological plasticity that thrives in urban, peri-urban and rural aquatic habitats. It is a major vector of West Nile virus (WNV), contributing to virus transmission among bird reservoirs and serving as a bridge vectorfor transmission to humans and mammals, which can result in neuroinvasive disease and fatalities. Controlling its populations reduces biting nuisance and associated economic and health burdens, making vector management essential for effective public health protection. Available methods to control this species are limited and require significant improvement because conventional strategies are often short-term, non-specific and ecologically problematic. The present study evaluated the efficacy of cyromazine granules on the Biodac carrier in laboratory, semi-field (in barrels) and field experiments (in canals). Content of cyromazine was 0.5 or 2%. Two formulations were tested: granules coated with stearate and uncoated granules. The highest efficacy was demonstrated by application of 2% cyromazine, both coated and uncoated, compared to the cyromazine with 0.5% active substance. Cyromazine showed high efficacy in the control of Cx. pipiens ranging from 85.8% to 100% in the laboratory, 68.1% to 100% in the semi-field and 48.1% to 98.8% in the field conditions (depending on the formulation applied), enabling long-lasting suppression of juvenile stages. In the laboratory, 53 days post-treatment, the residues were still present in the water. In the field experiment (in canals) the population reduction was recorded up to the 56th day post-treatment.