Seasonal variation in aquatic habitat availability and use by the malaria vector, Anopheles funestus

Larval source management (LSM) can be highly effective for controlling malaria vectors such as Anopheles funestus s.s., which typically exploit large and permanent aquatic habitats. While these habitats can persist year-round in endemic regions of Africa, their availability and use shift between wet and dry seasons. Understanding these seasonal changes is essential for identifying the habitats that sustain vector populations and for determining when and where LSM would be most effective.

We investigated the availability and use of An. funestus larval habitats across wet and dry seasons in south-eastern Tanzania, and the environmental factors that influence these patterns. Cross-sectional surveys were conducted in five villages during the dry season (September-November 2021) and rainy season (February-May 2022) to map and characterize aquatic habitats and identify those colonized by An. funestus.

In total, 2824 aquatic habitats were identified, of which 27% were positive for An. funestus. Remotely sensed land cover data and directly measured habitat characteristics were incorporated into generalized linear mixed models to evaluate seasonal and environmental predictors of larval presence and abundance. Larval occurrence and density were significantly influenced by habitat type, village, season, and their interactions, as well as by key physicochemical factors including water depth, vegetation type, algae, water clarity, and water source. An. funestus was commonly found in river streams, ground pools, and ditches across both seasons. During the wet season, however, it also occupied spring-fed wells, rice fields, and dug pits, indicating broader habitat use.

These findings demonstrate a clear seasonal shift in larval habitat use by An. funestus, reflecting its ecological adaptability. While the species generally favors permanent habitats, its expanded use of diverse sites in the wet season has important implications for LSM. Targeting persistent habitats during the dry season may offer a more efficient and feasible window for implementing this intervention.