Comparative attractiveness ofAnopheles quadriannulatusandAnopheles arabiensisto humans estimated by comparing the relative abundance of these two species in larval samples, unbaited adult catches and human-baited adult catches
Authors: Kavishe Deogratius R , Walsh Katrina A , Msoffe Rogath V , Duggan Lily M , Tarimo Lucia J , Butler Fidelma , Govella Nicodem J. , Kaindoa Emmanuel W. , Killeen Gerry F 
Published: August 2024

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 ofAnopheles arabiensisandAnopheles quadriannulatusto 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 adultAnopheles gambiaecomplex 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. arabiensiswas caught in greater numbers in the human-occupied tent, whileAn. quadriannulatuscatches remained consistently low across all traps, even in wild areas where it was dominant in larval population. The proportion ofAn. arabiensisin 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 beingAn. arabiensisrather thanAn. quadriannulatus. Similarly, the barrier trap away from humans but frequently visited by researchers showed a 24-fold enrichment ofAn. arabiensis.

These results confirm the strong attraction ofAn. arabiensisto humans, contrasting with the non-vectorAn. 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.