A comprehensive understanding of vector diversity, spatio-temporal distribution, and malaria transmission dynamics is fundamental for establishing effective vector control strategies. This study assessed entomological parameters across six sites in Niamey. Anopheles mosquitoes were collected using indoor residual spraying and CDC light traps during three seasons (rainy, cold, and hot). Specimens were identified morphologically and by PCR. Diversity was evaluated using ecological indices, while blood meal origin and Plasmodium infections were also detected by PCR. In total, 18,141 females Anopheles mosquitoes belonging to six species were collected: An. gambiaes.l., An. rufipes, An. funestus, An. pharoensis, An. nili, and An. ziemanni. An. gambiaes.l. was the predominant species complex, ranging from 96.62% to 99.68% across sites. Within the An. gambiae complex, two main species were identified: An. coluzzii (89.2%) and An. arabiensis (9.2%), along with 0.4% hybrids. These two anthropophagic species were the only ones found infected with Plasmodium, with infection frequencies varying by species, site, and season. The entomological inoculation rate (EIR) varied across sites, peaking during the rainy season (17.55 ib/p/m in Banigoungou versus 0.17 ib/p/m in Koira-Tegui) compared to lower values in the hot season (1.03 ib/p/m to 0.00). This study demonstrated that An. coluzzii and An. arabiensis are the principal malaria vectors in Niamey. Malaria transmission was found to be omnipresent, continuous, and particularly elevated during the rainy season and in riparian sites along the Niger River.
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