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Background  Aerial applications of insecticides that target adult mosquitoes are widely used to reduce transmission of West Nile virus to humans during periods of epidemic risk. However, estimates of the reduction in abundance following these treatments typically focus on single events, rely on pre-defined, untreated control sites and can vary widely due to stochastic variation in population dynamics and trapping success unrelated to the treatment.    Methods  To overcome these limitations, we developed generalized additive models fitted to mosquito surveillance data collected from CO 2 -baited traps in Sacramento and Yolo counties, California from 2006 to 2017. The models accounted for the expected spatial and temporal trends in the abundance of adult female  Culex   ( Cx. )  tarsalis  and  Cx. pipiens  in the absence of aerial spraying. Estimates for the magnitude of deviation from baseline abundance following aerial spray events were obtained from the models.    Results  At 1-week post-treatment with full spatial coverage of the trapping area by pyrethroid or pyrethrin products,  Cx. pipiens  abundance was reduced by a mean of 52.4% (95% confidence intrval [CI] − 65.6, − 36.5%) while the use of at least one organophosphate pesticide resulted in a mean reduction of 76.2% (95% CI − 82.8, − 67.9%). For  Cx. tarsalis , at 1-week post-treatment with full coverage there was a reduction in abundance of 30.7% (95% CI − 54.5, 2.5%). Pesticide class was not a significant factor contributing to the reduction. In comparison, repetition of spraying over three to four consecutive weeks resulted in similar estimates for  Cx. pipiens  and estimates of somewhat smaller magnitude for  Cx. tarsalis.Conclusions  Aerial adulticides are effective for achieving a rapid short-term reduction of the abundance of the primary West Nile virus vectors,  Cx. tarsalis  and  Cx. pipiens . A larger magnitude of reduction was estimated in  Cx. pipiens , possibly due to the species’ focal distribution. Effects of aerial sprays on  Cx. tarsalis  populations are likely modulated by the species’ large dispersal ability, population sizes and vast productive larval habitat present in the study area. Our modeling approach provides a new way to estimate effects of public health pesticides on vector populations using routinely collected observational data and accounting for spatio-temporal trends and contextual factors like weather and habitat. This approach does not require pre-selected control sites and expands upon past studies that have focused on the effects of individual aerial treatment events.

Spatio-temporal impacts of aerial adulticide applications on populations of West Nile virus vector mosquitoes