First evidence of resistance to pyrethroid insecticides in Italian Aedes albopictus populations 26 years after invasion

BACKGROUND: Aedes albopictus has spread during the last few decades all over the world. This has increased significantly the risk of exotic arbovirus transmission (e.g. chikungunya, dengue, and Zika) also in temperate areas, as demonstrated by the Chikungunya 2007 and 2017 outbreaks in northeastern and central Italy. Insecticides are an important tool for limiting the circulation of these mosquito-borne viruses. The aim of the present study was to address the gap in current knowledge of pyrethroid insecticide resistance of European Ae. albopictus populations, focusing on populations from Italy, Albania and Greece. RESULTS: Bioassays for resistance to permethrin (0.75%), α-cypermethrin (0.05%) or deltamethrin (0.05%) were performed according to World Health Organization (WHO) protocols and showed reduced susceptibility (