Past and present resistance status to pyrethroid insecticides of Aedes aegypti from New Caledonia

Dengue is a major public health concern in the Pacific region, including New Caledonia (NC), where control strategies have targeted Aedes aegypti for a long time. However, increasing insecticide resistance has reduced the effectiveness of these approaches. NC has recently implemented a Wolbachia -based strategy to reduce dengue transmission, though its success may be compromised by high resistance levels in local mosquito populations. We analyzed historical data from 92 Ae. aegypti lineages collected in Noumea between 2003 and 2018 and assessed 17 populations sampled across NC in 2020–2021 using WHO tube bioassays with deltamethrin. Resistance was evaluated through mortality rates and knockdown times. Molecular analyses identified kdr mutations in the VGSC gene and copy number variation at the 1011 locus were assessed. Deltamethrin resistance increased markedly over time, with median mortality declining from 95% to 46%. Recent populations showed widespread resistance, especially in urban areas. Two mutations, F1534C and I1011M, were detected. F1534C frequency increased substantially, while I1011M was only observed in heterozygotes and associated with gene duplication. Ouvea populations remained fully susceptible. These results indicate widespread resistance driven by specific mutations and gene duplication, highlighting the need to reconsider insecticide-based control and support alternative strategies such as Wolbachia .