Entomological Surveys in Rural Tanzania Reveal Key Opportunities for Targeted Larval Source Management to Control Malaria in Areas Dominated by Anopheles funestus

Background Larval Source Management (LSM) is re-emerging as a critical malaria intervention to address challenges associated with core vector control tools such as insecticide-treated nets (ITNs) and to accelerate progress towards elimination. Presently, LSM is not widely used in rural settings and is instead more commonly applicable in urban and arid settings. Here, we performed a systematic entomological assessment in rural communities of southeastern Tanzania, where ITNs are widely used, to explore opportunities for deploying LSM to improve malaria control. Methods Aquatic habitat surveys were conducted to understand habitat usage by different mosquito vectors, covering five villages during the rainy season of 2021, and seven villages during the dry season. Additionally, we sampled adult mosquitoes to assess the role of various Anopheles species in malaria transmission in the area and explore opportunities for species-targeted control. Results Adult mosquito surveys identified Anopheles funestus and Anopheles arabiensis as the main malaria vectors in the area, with total entomological inoculation rates (EIR) of 20.1 and 6.5 infectious bites per person per year indoors and outdoors respectively. An. funestus was responsible for over 97.6% of the malaria transmission indoors and 95.4% outdoors. The concurrent larval surveys found that habitats with late instar An. arabiensis and An. funestus comprised only a small subset of 11.2% − 16.5% of all water bodies in the rainy season, and 9.7% -15.2% in the dry season. In terms of size, these habitats covered 66.4% − 68.2% of the total habitat areas in the wet season, reducing to 33.9% − 40.6% in the dry season. From the rainy season to the dry season, the surface area of habitats occupied by An. arabiensis and An. funestus decreased by 92.0–97.5%, while the number of habitats occupied by An. arabiensis and An. funestus decreased by 38.0–57.3%. An. funestus preferred large, permanent habitats with clear water and vegetation year-round, while An. arabiensis showed contrasting seasonal preferences, favoring sunlit still waters in the rainy season and larger, opaque habitats in the dry season. Conclusion These findings suggest that An. funestus , which is the dominant malaria vector in the area, mediating over 95% of malaria transmission, preferentially occupies only a small subset of uniquely identifiable aquatic habitats in both wet and dry seasons. This presents an opportunity to expand LSM in rural settings by carefully targeting An. funestus habitats, which might be effective and logistically feasible as a complementary approach alongside existing interventions. Further research should assess the impact of such targeted LSM strategies compared to blanket LSM.