The daily and seasonal biting patterns of the vectors of enzootic, zoonotic and human malarias, Anopheles dirus and Anopheles maculatus, in North Sumatra, Indonesia

Zoonotic malaria cases in humans are increasing across Southeast Asia including in Indonesia, but the vectors’ transmission dynamics are still poorly understood. Incriminating the vector species and defining their behaviours is essential to understanding zoonotic malaria transmission and to develop effective control strategies based on targeting vector behaviours that make them vulnerable to different interventions. Adult mosquito collections were conducted from July 2022 to June 2023 using all-night human landing collections in two hamlets (dusun) encompassing three land-use settings (oil palm plantations, residential areas, and mixed plantation areas) within Ujung Bandar village in Sumatra, Indonesia. Each sampling station was characterised for vegetation density and composition for possible associations with mosquito populations. Biting rates of Anopheles dirus were highest in the mixed plantation area surrounded by fragmented forest of Dusun 5 (mean bites/man-hour = 2.98 [95% CI ± 1.23]), while Anopheles maculatus biting rates were highest in the oil palm plantation in Dusun 2 (mean bites/man-hour = 0.90 [95% CI ± 0.43]). In residential settings, An. dirus exhibited higher biting rates than An. maculatus. Anopheles. dirus biting rates were higher in sampling stations in mixed plantations with a high density of herbs while An. maculatus numbers were higher in sampling stations in oil palm plantations with higher shrub densities. Anopheles dirus and An. maculatus mosquitoes, potential vectors of human and simian malarias in North Sumatra, Indonesia, exhibited outdoor biting throughout the night, with peak biting rates occurring before midnight. The highly exophagic biting behaviours of An. dirus found in the two dusuns sampled in this study suggests that insecticide treated nets and indoor residual spraying will have limited effects on the transmission of zoonotic and human malarias by An. dirus. These findings highlight the importance of considering vector behaviours when designing malaria control strategies in zoonotic transmission settings.