Metabolic resistance drives cross-resistance in Aedes albopictus to pyriproxyfen and pyrethroid insecticides.

Aedes albopictus is a major global vector of arboviruses. Pyriproxyfen, an insect growth regulator, is increasingly used for mosquito control, but the potential for resistance and cross-resistance with pyrethroids poses a serious threat. Through 13 generations of laboratory selection, we established a highly pyriproxyfen-resistant Ae. albopictus strain (Lab-R, RR50 = 10.12). This strain developed moderate to high cross-resistance to the permethrin, deltamethrin, and beta-cypermethrin (RR50 = 8.11-10.30). Resistance was associated with significant fitness costs, including prolonged larval development, reduced female longevity, and lower fecundity and egg hatching. Crucially, resistance of Lab-R was driven by enhanced metabolic enzyme activity (P450s, GSTs, Car Es), with no target-site mutations detected in the CHS-1 or kdr genes. Synergist assays confirmed that enzyme inhibitors largely restored insecticide susceptibility. These findings demonstrate that metabolic resistance mediates cross-resistance between pyriproxyfen and pyrethroids in Ae. albopictus, carrying substantial fitness trade-offs. For vector control programs, this warns against the overreliance on rotational or sequential use of pyriproxyfen and pyrethroids as the sole rotation strategy, emphasizes the need for routine monitoring of metabolic resistance, and supports the potential use of synergists such as PBO to restore efficacy where resistance has emerged.