Carbon dioxide (CO
2) is an important component for activating and attracting host-seeking mosquitoes. The BG-Sentinel® trap is a well-established monitoring tool for capturing Culicidae, but CO
2 role for the trap effectiveness has not been evaluated in highly urbanised areas. The objective was to evaluate the effectiveness of BG-Sentinel traps baited with and without CO
2 for capturing urban mosquitoes. Fifteen areas were selected within the city of Manaus, Brazil, where four BG-Sentinels were operated for 24 h, two of them with CO
2 and two without CO
2. Captured
Aedes aegypti
females were dissected for the determination of their parity status. A significantly higher proportion of traps (from 32-79%) were positive for female
Ae. aegypti when using the BG-Sentinel with CO
2 (χ2 = 11.0271, p < 0.001). Catches of female
Culex spp were six times higher in CO
2 traps (Mann-Whitney U test = 190.5; p = 0.001). Parity rates were similar for both traps. This study showed that CO
2 has primarily an enhancing effect on the efficacy of BG-Sentinel for capturing
Culex spp in Manaus. For
Ae. aegypti, the positivity rate of the trap was increased, when CO
2 was added.