Impact of Cypermethrin persistence on stomoxyine abundance and Trypanosoma Vivax infection

Stomoxyine biting flies play a pivotal role as mechanical vectors of Animal African Trypanosomosis (AAT), inducing painful bites and significant disturbances in cattle, thereby affecting productivity. This study delves into the dynamics of cypermethrin persistence on cattle, a key measure aimed at mitigating stomoxyine populations and the associated transmission of trypanosomes. Conducted within a cattle settlement in Ido, Ibadan, southwest Nigeria, data collection occurred biennially from 2016 to 2022. Cypermethrin application followed a restricted protocol triggered by high fly density. Stomoxyine flies were systematically trapped every three months over a five-day period, employing four Nzi traps per collection cycle. The flies were taxonomically categorised, and their relative abundance assessed. Additionally, engorged flies underwent ITS-PCR analysis to detect T. vivax presence in their mouthparts. The investigation unveiled a noteworthy decline in cypermethrin persistence from 10.7 to 4.9 days over the six-year span, significantly influencing stomoxyine population dynamics and T. vivax infection rates. Despite escalated cypermethrin utilisation, stomoxyine abundance exhibited stability, hinting at potential insecticidal resistance. Notably, cypermethrin persistence was at its highest during July-September, aligning with heightened rainfall and humidity conducive to stomoxyine larval development. The heightened probability of detecting T. vivax DNA in stomoxyine flies as cypermethrin persistence dwindled underscores the intricate interplay between reduced insecticide efficacy and heightened pathogen dissemination. This underscores the imperative for integrated, enhanced control strategies considering the prevailing T. vivax resistance to trypanocides and diminishing cypermethrin efficacy.