We conducted an open-field ultra-low volume efficacy bioassay using a water-based formulation AquaDuet™ (prallethrin [1%], sumithrin [5%], and piperonly butoxide [5%]) applied from a truck-mounted cold aerosol sprayer. The adulticide was applied at 90.6 ml/ha (1.23 oz/acre) and 3 replicated treatments were performed using caged Aedes albopictus collected from local wild populations. Rotating impingers and mosquito cages were placed in 3 rows stationed at 30.5 m (100 ft), 61.0 (200 ft), and 91.4 (300 ft) downwind of the spray vehicle. Initial knockdown was 95.6%, with overall mortality >99% across all distances, despite low wind conditions. Volume median diameter (Dv_0.5) and droplet density were 17.4 µm and 110.5 mm², respectively. Our open-field studies against caged Ae. albopictus demonstrate that a water-based adulticide formulation is just as efficacious as traditional oil-based formulations.