Comparison of insecticide resistance of Aedes albopictus before and after dengue fever epidemic in Ningbo, Zhejiang

  Objective  To investigate the resistance of Aedes albopictus to common insecticides before and after the dengue fever epidemic in Ningbo, Zhejiang province, and provide a scientific evidence for resistance management and dengue fever control.

  Methods  Ae. albopictus larvae were collected in 10 counties (districts) in Ningbo before the epidemic of dengue fever in 2018 and after the epidemic in 2019. The collected larvae were reared for 1–2 generations in laboratory. The resistance of larvae and adults was determined by dipping method and contact method, respectively.

  Results  The resistance ratios of Ae. albopictus larvae to deltamethrin, beta-cypermethrin, propoxur, dichlorvos and temephos were 45.43, 18.85, 4.81, 1.55 and 4.13 in 2018, respectively, and 82.00, 29.43, 7.14, 3.27 and 6.25 in 2019, respectively. Ae. albopictus adults exposed to 0.4% beta-cypermethrin, 0.1% deltamethrin, 3% permethrin, 0.05% propoxur and 0.5% malathion for 1 h, the death rates were 98.33%, 83.33%, 88.52%, 95.24% and 76.67% 24 h later in 2018, respectively, and 98.89%, 92.22%, 98.89%, 100.00% and 98.89% 24 h later in 2019, respectively.

  Conclusion  Ae. albopictus larvae in Ningbo developed resistance to the tested insecticides, which was significantly higher than that before the dengue fever epidemic. While adult mosquitoes were relatively sensitive to the tested insecticides, and the resistance did not significantly increase. The insecticide resistance levels of larvae and adult mosquitoes were not consistent, so appropriate insecticide use strategies should be adopted for mosquito control according to the insecticide resistance of Ae. albopictus at different growth stage.