VU041 is a first submicromolar-affinity inhibitor of Anopheles (An.) gambiae and Aedes (Ae.) aegypti inward rectifier potassium 1 (Kir1) channels with IC50 values of 2.5?μM and 1.7?μM, respectively. VU041 inhibits appreciably is mammalian Kir2.1 (IC50 of 12.7?μM), and has less inhibitory effect on mammalian Kir1.1, Kir4.1, Kir6.2/SUR1, and Kir7.1. VU041 also induces impaired Malpighian tubule function.IC50 & Target: IC50: 2.5?μM (Anopheles (An.) gambiae Kir1 channels), 1.7?μM (Aedes (Ae.) aegypti Kir1 channels) and 12.7?μM (Mammalian Kir2.1)In Vitro: VU041 is only moderately metabolized by cytochrome P450 enzymes and does not appear to be metabolized by esterases. VU041 is the first small-molecule inhibitor of mosquito Kir1 channels that exhibits topical toxicity in both insecticide-susceptible and -resistant lines of mosquitoes.In Vivo: Topical VU041 application to adult female mosquitoes of both species inhibits their fecundity. Importantly, VU041 is selective for mosquito Kir channels over mammalian Kir channel orthologs and non-lethal to adult honey bees (Apis mellifera). The in vivo experiments of blood meal processing and diuretic capacity suggest that one mechanism of action of VU041 is the disruption of excretory functions mediated by Malpighian tubules.