Determination of the resistance of adult Culex pipiens pallens to commonly used pesticides in Jiangsu province

Objective To determine the current resistance of adult Culex pipiens pallens to commonly used pesticides in Jiangsu province, providing the evidence for better mosquito control. Methods The exposure tube method recommended by WHO was applied to measure the median lethal concentration (LC50) for adult mosquitoes. Results The LC50 for field-collected adult mosquitoes in Nanjing, Xuzhou, Lianyungang, Wuxi, Nantong and Huai’an were 0.0173%, 0.0756%, 0.0487%, 0.0070%, 0.0055% and 0.0150% to deltamethrin respectively, and 0.2128%, 0.2711%, 0.1130%, 0.1579%, 0.0504% and 0.0734% to permethrin, respectively. The LC50 to betacypermethrin for field populations in Nanjing, Xuzhou, Lianyungang, Wuxi, Nantong, Huai’an and Suzhou were 0.0224%, 0.0420%, 0.0843%, 0.0023%, 0.0114%, 0.0180% and 0.0108% respectively. The LC50 for Nanjing population to dichlorovos and propoxur were 0.0119% and 0.0129%, while the values for Nantong population to dichlorovos and propoxur were 0.0046% and 0.0077%, respectively. All of tested mosquitoes were intermediately to highly resistant to deltamethrin, with resistance coefficients greater than 100 times in Xuzhou and Lianyungang; lowly to highly resistant to betacypermethrin, with the resistance coefficient up to 94.7 times in Lianyungang in contrast to 2.6 times in Wuxi; and lowly to intermediately resistant to permethrin, with resistance ratios ranging from 11 to 15 times in Nanjing and Xuzhou, and 2.8 times in Nantong. Nanjing population were lowly resistant to propoxur (2.8 times) and sensitive to dichlorovos, while Nantong strains were susceptible to both propoxur and dichlorovos. Conclusion For adult mosquito control in Jiangsu province, the application of deltamethrin and betacypermethrin should be reduced along with increased administration of carbamates, such as propoxur, and organophosphorus pesticides such as dichlorovos. The findings here address consideration and integrated planning to chemical adult mosquito control for delaying or reducing the occurrence and development of pesticid resistance.