Simple SummaryFailure to control nuisance mosquitoes may potentially affect adherence to vector control tools. In the present study, we examined the impact of two dual-active ingredient (a.i.) long lasting insecticidal nets (LLIN), namely Interceptor G2®LLIN (alpha-cypermethrin-chlorfenapyr LLIN) and Royal Guard®LLIN (alpha-cypermethrin-pyriproxyfen LLIN), on the density ofCulexandMansoniamosquito species as compared to Interceptor®LLIN (alpha-cypermethrin-only LLIN). The study took place over two years in 60 clusters in the Zou region, Benin, with 20 clusters assigned to each of three study arms. Entomological data were collected over nine rounds up to 24 months post-net distribution. Overall, there was no evidence of a significant reduction in the density ofCulexspp. AndMansoniaspp. in the two dual-a.i. LLIN arms compared to the pyrethroid-only net. Both mosquito genera were found to bite more outdoors, with similar magnitudes of reduction observed in all three study arms in year 2 compared to year 1. Our findings suggest that the three types of LLINs had similar effects on the density ofCulexspp. andMansoniaspp. Going forward, the development of interventions which provide control of outdoor biting mosquitoes also needs to be prioritized.AbstractThe efficacy of a vector control tool in reducing mosquito biting is crucial for its acceptability. The present study compared the vector density ofCulexspp. AndMansoniaspp. across clusters, which received two dual-active ingredient (a.i.) long-lasting insecticidal nets (LLINs) and a standard pyrethroid-only LLIN, and assessed the seasonality of these mosquito genera. A total of 85,723Culexspp. and 144,025Mansoniaspp. were caught over the study period. The density ofCulexandMansoniawas reduced in all three arms over the study period. There was no evidence of a significant reduction in the indoor or outdoor density ofCulexspp. in either dual-a.i. LLIN arm as compared to the standard pyrethroid-only net arm. A similar trend was observed withMansoniaspp. A high density ofCulexspp. was found both in rainy and dry seasons, while forMansoniaspp., this was mainly observed during the rainy season. These results suggest that the novel insecticides in the dual-a.i. LLINs did not have an additional impact on these species and that pyrethroids might still be effective on them. Further work is required to determine whether these species of mosquitoes have resistance to the insecticides tested in this trial.