To determine the vector competence of Cx. pipiens and An. plumbeus, mosquitoes were exposed to a blood meal containing 7.1×10^7 PFU/mL WNV (strain Israel 98, lineage 1) and incubated for 14 days at either a constant temperature of 25°C, or a temperature gradient of 25/20°C or 25/15°C. Infection rates (IR), dissemination rates (DR) and transmission rates (TR) were determined by detection of viral RNA via qRT-PCR in abdomen, head-wings-legs and saliva, resp. Results indicated that at a constant 25 °C, Cx. pipiens had an IR of 28%, DR of 53%, and TR of 50%. Similar IR (25%) and DR (60%) were found for An. Plumbeus, although the TR was lower (11%). Temperature gradients had no significant impact on the IR, DR and TR rates of Cx. pipiens for WNV compared to the 25°C condition. In An. plumbeus, no effect was seen of the temperature gradients on the IR, but the DR was significantly reduced at the 25/15°C condition (10%). No WNV could be detected in the saliva in any of the An. plumbeus mosquitoes at the gradient temperatures. These findings suggest that both species are competent vectors for WNV at 25°C, with overall transmission efficiencies of 7.4% (Cx. pipiens) and 1.6% (An. plumbeus). When temperature gradients are introduced, representing current Belgian summer conditions, An. plumbeus loses its vector competence for WNV. In contrast, Cx. pipiens remains a competent vector at both the 25/20 °C and 25/15°C gradient with transmission efficiencies of 1,4% and 7.8%, resp.