Matsuda, I.; Manin, B. O.; Yahiro, T.; Lambut, P.; Tangah, J.; Huffman, M. A.; Bernard, H.; Subbiah, V. K.; Chua, T. H.

Understanding how vector ecology intersects with host behaviour is essential for predicting zoonotic disease risk in tropical ecosystems. We conducted a two-year field study (November 2016-October 2018) in a riverine forest in Sabah, Malaysian Borneo, to characterize mosquito communities and the spatial distribution of potential simian-malaria vectors. Mosquitoes were sampled on 44 nights using CO2-baited light traps repeatedly deployed along a 500 m transect at three distances from the river (0, 250, 500 m) and two vertical strata (ground and canopy), yielding 244 trap collections across repeated sampling nights. In total, 9,928 mosquitoes were collected, dominated by Culex spp. (9,079; 91.4%), whereas Anopheles spp. were rare (153; 1.5%); most remaining specimens were unidentified to genus, and species-level identification was limited primarily to Anopheles. Nevertheless, female Anopheles (n=57) were more frequently detected near the river and less commonly at intermediate distance, and tended to be captured more often in ground traps. Zero-inflated negative binomial GLMMs based on the full mosquito dataset indicated significant effects of river distance and height on mosquito abundance, while night-time temperature and humidity showed no detectable effects. The zero-inflated structure of the data further suggested that many zero captures reflected true absence rather than sampling variability. The Anopheles assemblage was dominated by An. balabacensis, and molecular screening of 57 females detected simian Plasmodium DNA in two individuals. Overall, these findings suggest that river-edge habitats may represent localized areas where vectors persist and where primates and human activities overlap, creating repeated opportunities for host-vector contact even when vector densities are low.