Larval habitat preferences of Anopheles dirus and Anopheles maculatus in North Sumatra, Indonesia

While human malaria transmission in Indonesia has declined, reported cases of zoonotic Plasmodium knowlesi are increasing. This study examined the larval habitats of malaria vectors in North Sumatra to assess the potential of larval source management as a control strategy for both human and zoonotic malaria vectors.

Multiple larval habitat surveys in the areas surrounding two dusuns with documented human and zoonotic (P. knowlesi) malaria cases in Langkat Regency, North Sumatra, were conducted over 2 years, encompassing both wet and dry seasons. Larval habitats were characterized by mosquito immature presence and density, land-use type where found, aquatic habitat class (i.e., naturally occurring, man-made from natural materials or man-made from artificial materials), and habitat subclass for a range of abiotic and biotic parameters.

A total of 1413 mosquito larvae and 98 pupae were collected. Anopheles larvae comprised 20.6% of all mosquito immatures. Anopheles maculatus comprised 65.3% of all immature anophelines, followed by Anopheles dirus (21.9%), Anopheles scanloni, Anopheles kochi, and Anopheles vagus in order of abundance. Habitat class predicted anopheline presence and density, with larvae occurring more frequently in naturally occurring habitats and man-made habitats from natural materials than in artificial man-made habitats (presence: generalized linear mixed model [GLMM] β =  -1.45, P = 0.006; density: β =  -1.42, P = 0.001). At the habitat subclass level, An. maculatus larvae were most frequently detected in natural habitats, particularly stream margins. Meanwhile, An. dirus larvae occurred approximately equally in natural habitats and man-made habitats from natural materials, with tire tracks being the most common habitat subclass. Four species (An. maculatus, An. dirus, An. scanloni, and An. kochi) were detected, albeit infrequently, in man-made habitats from artificial materials.

In North Sumatra, anopheline vector species utilize a diverse range of larval habitats, including natural and man-made, on both natural substrates and artificial materials. Species-specific habitat preferences were observed: An. dirus was found in both natural and man-made habitats from natural materials, whereas An. maculatus was predominantly found in more dispersed and inaccessible natural sites, suggesting that larval control may be more challenging for An. maculatus than An. dirus.