Resistance of Aedes albopictus to commonly used chemical insecticides in a county of Jining City, Shandong

ObjectiveTo investigate the resistances of larva and adult of Aedes albopictus to common insecticides in a county of Jining City, after the dengue fever outbreak in 2017, and to provide scientific support for rational use of insecticides.

MethodsThe insecticide resistance was tested with exposure tubes for adult mosquitoes and dipping method for larvae.After collecting the larvae and breeding for one generation, the resistances of larvae were determined with the late third-instar or early fourth-instar larvae, and the resistance of adults was tested with the female mosquitoes at 3-5 days post eclosion.

ResultsThe insecticides mainly used in the county of Jining City in 2018 were pyrethroids such as permethrin, β-cyhalothrin, α-cypermethrin, and organic phosphorus pesticides such as phoxim.The median lethal concentration (LC₅₀) values in the larva to temephos, deltamethrin, permethrin, beta-cypermethrin were 0.006 mg/L(RR=3.75), 0.021 mg/L(RR=52.50)、0.209 mg/L(RR=104.50)、0.016 mg/L (RR=17.78), with the lowest resistance to temephos and the highest to permethrin.Adult mosquitoes were sensitive to permethrin, with a knockdown rate of 97.62% and a mortality rate of 100%.When exposed to propoxur and malathion, the knockdown rates were 97.06% and 91.89%, the mortality rates were 97.06% and 93.24%.Aedes albopictus larvae were resistant to deltamethrin, α-cypermethrin, β-cyhalothrin, β-cypermethrin, with the knockdown rates of 88.00%, 95.31%, 91.04%, 97.10%, and the mortality rates were all less than 80.00%.

ConclusionThe larvae and adult mosquitoes of Aedes albopictus in the county of Jining City have developed different degrees of resistance to commonly used insecticides.The resistance should be under regular monitoring and the use of insecticides should be scientific and rational to delay the resistance production.