Comparative attractiveness of Anopheles quadriannulatus and Anopheles arabiensis to humans estimated by comparing the relative abundance of these two species in larval samples, unbaited adult catches and human-baited adult catches.

Abstract

Understanding mosquito vector behaviour, abundance, and bionomics is crucial for effective malaria prevention. Since most malaria parasites in humans are strict anthroponoses, mosquito preference for humans as a blood source is a key determinant of transmission intensity and intervention strategies. This study compares the attraction of Anopheles arabiensis and Anopheles quadriannulatus to humans by assessing their relative abundance in larval samples and adult mosquito catches using unbaited and human-baited traps. The research investigated how the abundance of these sibling species varies with the local availability of humans, livestock, and wildlife as potential blood sources. Surveys of larval and adult mosquito populations were conducted at 40 mobile camping locations distributed across a landscape mosaic of different habitat types, with a gradient of land use practices ranging from comprehensive conversion to agriculture and human settlement to essentially intact natural ecosystems inside well-protected conservation areas. Larvae were collected from all accessible water bodies within a 2 km radius of each mobile camp, while adults were surveyed using four light traps and one interception netting barrier trap at each camp. Light traps were strategically placed at locations such as beside a human-occupied tent, near the camp, in a nearby streambed, and in an open natural glade, while the netting barrier trap was placed in the open natural glade. Most adult Anopheles gambiae complex mosquitoes caught were unfed and presumably host-seeking. The mean catches of the complex in light traps next to the human-occupied tent was over four times higher than elsewhere around the camp (p<<0.0001). Catches decreased with distance from humans, suggesting attraction to humans by at least one species in the complex. An. arabiensis was caught in greater numbers in the human-occupied tent, while An. quadriannulatus catches remained consistently low across all traps, even in wild areas where it was dominant in larval population. The proportion of An. arabiensis in adult collections was higher than in larval samples (98.7% versus. 78.3%, p<<0.0001), and adults caught beside human-occupied tents had 36 times higher odds of being An. arabiensis rather than An. quadriannulatus. Similarly, the barrier trap away from humans but frequently visited by researchers showed a 24-fold enrichment of An. arabiensis. These results confirm the strong attraction of An. arabiensis to humans, contrasting with the non-vector An. quadriannulatus, which is largely unresponsive to humans. Light traps by human-occupied tents efficiently capture anthropophagic mosquitoes outdoors, while unbaited traps far from people appear to give unbiased representations of larval population composition but with very low efficiency. Moreover, netting barriers with human activity attract anthropophagic mosquitoes, turning them into semi-baited traps with moderate efficiency.