The impact of Bacillus thuringiensis var israelensis (Bti) larvicide sprayed using drones for bio-control of malaria vectors in rice fields of Kigali Sub-Urban, Rwanda

Background The core vector control tools used to prevent malaria infection are currently long-lasting insecticide treated nets (LLINs), and the indoor residual spraying (IRS). These indoor methods are threatened by insecticide resistance and behavioral adaptation by malaria vectors. Thus, for effective interruption of malaria transmission, there is a need to experiment further vector control interventions and technologies to address the above vector control challenges. Larviciding using drones-based technologies were experimented as innovative tools that could supplement existing indoor base interventions to control malaria. Methods A non-randomized larviciding trial with control was carried out in irrigated rice fields, in sub-urban of Kigali City, Rwanda. The potential mosquito larval habitats in study sites were prior mapped and subsequently sprayed using multirotor drones. The application of Bti (Vectobac® WDG) followed by the entomological surveys were performed every two weeks for ten months’ period. The sampling of mosquito larvae used the dipping method while adult mosquitoes were collected using CDC miniature light traps (CDC-LT) and pyrethrum spraying collection (PSC) methods, respectively. The malaria cases were routinely collected through community health workers in contingent villages to the study sites. Results The abundance of total mosquito larvae, Anopheles -specific larvae and pupae declined by 68.1%, 74.6% and 99.6% respectively. The larval density was reduced by 93.3% for total larvae, 95.3% for the Anopheles larvae and 61.9% for pupae. The total adult mosquitoes and An. gambiae s.l collected using CDC-Light trap declined by 60.6% and 80% respectively. Malaria incidence also declined significantly between intervention and control sites (U=20, z=-2.268, p=0.023) Conclusions The larviciding using drone technology implemented in Rwanda demonstrated a substantial reduction in abundance and density of mosquito larvae and, concomitant decline in adult mosquito populations and malaria incidence in contingent villages to the treatment sites. The impact of PSC method on adult mosquitoes was not significant on adult culicines spp. The scaling up of larval source management (LSM) has to be integrated in malaria programs in targeted areas of malaria transmission in order to enhance the gains in malaria control.