Trends in insecticide resistance in Culex pipiens pallens over 20\xa0years in Shandong, China

Hongmei Liu,Jiabao Xu,Xiaodan Huang,Jingxuan Kou,Lihua Xie,Lijuan Liu,Xiao Song,Guiyun Yan,Xiao-Guang Chen,Haifang Wang,Huaiwei Wang,Maoqing Gong,Peng Cheng

doi:10.1186/s13071-019-3416-9

Abstract

BackgroundCulex pipiens pallens is the most abundant Culex mosquito species in northern China and is an important vector of bancroftian filariasis and, potentially, West Nile virus. Insecticides, particularly pyrethroids, are widely used for adult mosquito control. Insecticide resistance has become common in several mosquito species, and vector control is the main method currently available to prevent disease transmission. The voltage-gated sodium channel (Vgsc) gene is the target site of pyrethroids, and mutations in this gene cause knockdown resistance (kdr).MethodsCulex pipiens pallens larvae were collected from May to November over two decades, from 1992 to 2018, in four cities in Shandong Province, China. The World Health Organization (WHO) standard resistance bioassay was applied to test the resistance levels of Cx. p. pallens larvae to five different insecticides and to test deltamethrin resistance in adults, using the F1 generation. Mutations at Vgsc codon 1014 were also screened in 471 adult samples collected in 2014 to determine the association between kdr mutations and phenotypic resistance.ResultsLarval resistance against deltamethrin showed an increasing trend from the 1990s until 2018, which was statistically significant in all populations; resistance to cypermethrin increased significantly in mosquitoes from the Zaozhuang population. However, larval resistance to other insecticides remained relatively stable. Larval resistance against deltamethrin was consistent with adult bioassays in 2014, in which all tested populations were highly resistant, with mortality rates ranging from 39.4 to 55.23%. The L1014S and L1014F mutations were both observed in five Cx. p. pallens populations, with L1014F significantly associated with deltamethrin resistance.ConclusionsThe long-term dataset from Shandong demonstrates major increases in pyrethroid resistance over a 20-year period. The L1014F kdr mutation may be considered a viable molecular marker for monitoring pyrethroid resistance in Cx. p. pallens.

Highlights

Culex pipiens pallens is the most abundant Culex mosquito species in northern China and is an impor‐ tant vector of bancroftian filariasis and, potentially, West Nile virus
We found that the frequency of the L1014F mutation was significantly higher in the R population than that in the S population for all four populations (Table 4)
There is an urgent need for the development of a surveillance plan for pyrethroid resistance and countermeasures to control the spread of resistance, as a wide distribution of the kdr mutations was found in Cx. p. pallens mosquitoes

Summary

Introduction

Culex pipiens pallens is the most abundant Culex mosquito species in northern China and is an impor‐ tant vector of bancroftian filariasis and, potentially, West Nile virus. Insecticide resistance has become common in several mosquito species, and vector control is the main method currently available to prevent disease transmission. Culex pipiens pallens is widely distributed in China [1, 2] This species usually occurs at a high density near humans and can transmit bancroftian filariasis and Japanese encephalitis. Culex pipiens pallens is a potential vector of West Nile virus (WNV) in China [3]. Pyrethroids are the principal class of insecticide approved for use on ITNs and are the most widely employed insecticide for vector control programs due to their low mammalian toxicity and rapid knockdown action [5].

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Conclusion