Mosquitoes are problematic as vectors and pests in many tropical cities, including Darwin, the principal city in the Northern Territory of Australia. To monitor peaks in mosquito populations, the Medical Entomology unit of the Health Department sets overnight CO2-baited traps weekly. Trap setting and retrieving, followed by mosquito counting and identification, are labor intensive. Aiming to reduce this workload, we tested the hypothesis that fortnightly trapping is as effective as weekly trapping across seasons and ecologically distinct systems in Darwin. We applied cross-sectional negative binomial mixed effects models, which adjusted for rain and calendar month, to existing historical data. Culex annulirostris peaks were effectively identified using fortnightly trapping across all three ecological systems, during wet/dry and build-up seasonal patterns. For Aedes vigilax, fortnightly trapping was adequate in identifying peaks during wet and dry season months, but inadequate during build-up months across all three ecological systems. Therefore, weekly trapping should continue during build-up months, but trapping could be reduced to fortnightly for wet and dry season months for all ecological systems. Trapping for Cx. annulirostris monitoring could be reduced to fortnightly in all areas and seasons. Evaluation of programs can maximize staff efficiency and improve service delivery by reducing the need for unnecessary tasks.