Fine-scale spatio-temporal dynamics of kdr mutation V1016G in Aedes albopictus along a transect encompassing the Rome metropolitan area.

Pyrethroid insecticides are largely exploited in Italy to reduce Aedes albopictus nuisance and to discontinue autochthonous transmission of exotic arboviruses. V1016G mutation in the voltage-gated sodium channel gene is strongly associated with resistance to pyrethroids in this species. Here, we provide an unprecedented high-resolution spatiotemporal analysis of the distribution/frequency of the V1016G mutation over an 11-year period in Ae. albopictus populations sampled across a transect encompassing the eco-geographical variability of Mediterranean Europe, including Rome, the only European metropolitan area that has experienced both dengue and chikungunya outbreaks. The results reveal marked spatial heterogeneities in 1016G frequencies, with the highest values in a coastal tourist town (47.7%) and in a few sites within Rome (up to 38.5%), as well as an 8.7% mean increase in allele frequency from 2012 to 2023. Frequency increases in samples collected in the early vs late 2023 season were also observed, particularly in some of the sampling sites. Overall, the results highlight a complex spatio-temporal pattern which is likely due to the trade-off between heterogeneous selective pressure, the effect of gene flow between populations exposed to different levels of pyrethroid spraying and a possible fitness cost of the 1016G allele. Frequencies up to 20% of GG homozygotes detected in some sites underline a possible risk of a reduction in the full effectiveness of pyrethroid treatments implemented in case of autochthonous arbovirus transmission, which - if confirmed phenotypically - should prompt the development of pyrethroid resistance management plans.