Insecticide resistance of adult Aedes albopictus in Huzhou City of Zhejiang Province from 2019 to 2020

ObjectiveTo investigate the resistance level of adult Aedes albopictus to commonly used insecticides in urban areas of Huzhou City， and analyze the trend of insecticide resistance.MethodsAedes albopictus larvae were collected from different urban areas of Huzhou City in 2019 and 2020. The larvae were reared to adults for determining resistance using the WHO standard test kits by contact tube method.ResultsThe mortality was 97.06%‒100.00% in adult Aedes albopictus mosquitoes exposed to 0.4% beta-cypermethrin， 0.1% deltamethrin， 0.5% malathion， 0.05% propoxur and 3% permethrin in 2019. While the adult mosquitoes exposed to 0.4% beta Cypermethrin， 0.08% beta Cypermethrin， 0.03% deltamethrin， 0.4% permethrin， 0.5% malathion and 0.02% propoxur in 2020， the adjusted mortality were 98.58%， 89.09%， 85.64%， 91.34%， 91.43% and 100% respectively . When the insecticide doses on medicated paper were high， the Huzhou populations of Aedes albopictus were sensitive to beta-cypermethrin， deltamethrin， malathion and propoxur， and showed suspected resistance to permethrin. While the Aedes albopictus were exposed to low testing dose， they showed suspected resistance to beta-cypermethrin， deltamethrin， permethrin and malathion， but remained to be sensitive to propoxur.ConclusionThe adult Aedes albopictus in Huzhou City from 2019 to 2020 was still sensitive to propoxur， but their resistance to malathion changes from sensitive to resistant. When the contact tube method is used for insecticide resistance， it is suggested that the accurate diagnostic dose should be obtained first before conducting further insecticide resistance tests.