The beta-triketone, nitisinone, kills insecticide-resistant mosquitoes through cuticular uptake
The efficacy of numerous vector control initiatives is compromised by growing insecticide resistance among disease-transmitting arthropods of agricultural, veterinary, and public health significance. Previous investigations on hematophagous (blood-feeding) arthropod vectors, including mosquitoes, have indicated that ingesting blood containing inhibitors of the second enzyme in the tyrosine metabolism pathway, 4-hydroxyphenylpyruvate dioxygenase (HPPD), results in high insect mortality. Building upon this foundation, we evaluated the insecticidal efficacy of the HPPD inhibitor, nitisinone, against susceptible and pyrethroid-resistant strains of three mosquito species: Anopheles gambiae, Aedes aegypti and Culex quinquefasciatus. These mosquitoes are vectors of historical diseases such as malaria, emerged diseases such as Dengue and Zika and emerging viral diseases such as the Oropouche and Usutu viruses. We demonstrate, by employing standard screening assays designed to assess the cuticular uptake of mosquitocidal agents, that nitisinone has mosquitocidal activity when blood-fed mosquitoes contact a nitisinone-coated surface. Notably, there is no discernible disparity in susceptibility to nitisinone between an insecticide-susceptible strain of Anopheles gambiae and two strains carrying multiple insecticide-resistance mechanisms. We conclude that the mosquitocidal mode of action of nitisinone differs from any of the current 37 classes of insecticides as none have a mode of action that specifically interferes with blood digestion. By highlighting the efficacy of nitisinone as a contact-based insecticide, our findings support the potential expansion of vector control strategies where nitisinone is incorporated into classic interventions like treated bednets and indoor residual spraying.