Resistance of Blattella germanica to five insecticides in Zhejiang Province,China,2017-2022
Objective To investigate the resistance levels of Blattella germanica to five commonly used insecticides in Zhejiang Province,China,so as to provide a basis for rational use of insecticides and scientific control of cockroaches.Methods From 2017 to 2022,field population of B.germanica were collected in different surveillance areas of Zhejiang Province in different years.The resistance of B.germanica to beta-cypermethrin,deltamethrin,acephate,dichlorvos,and propoxur was measured by using the residual film method with a conical flask.The median knockdown time and resistance ratio(RR)were calculated using a probit regression model.Results From 2017 to 2022,the overall resistance of B.germanica to pyrethroid insecticides was relatively high in Zhejiang Province.The RR for beta-cypermethrin was 11.49 in Jinhua in 2022,6.48 in Shaoxing in 2021,16.00 in Wenzhou in 2018,and 6.87 in Lishui in 2018,indicating medium-to-high resistance levels.The RR for deltamethrin was 8.66 in Quzhou in 2020,10.20 in Wenzhou in 2017,11.66 in Jinhua in 2018,and 7.58 in Lishui in 2018,showing medium-to-high resistance levels.The RR for dichlorvos was 7.86 in Jinhua in 2022,7.33 in Shaoxing in 2021,and 7.05 in Wenzhou in 2017,showing medium resistance levels.In general,B.germanica was sensitive or lowly resistant to acephate and propoxur in Zhejiang Province.B.germanica developed from sensitive to lowly resistant to propoxur in Ningbo since 2020,developed moderately resistant to deltamethrin in Quzhou since 2020,and developed from sensitive to moderately or lowly resistant to both pyrethroids and dichlorvos from 2018 to 2021.In 2022,insecticide resistance levels were higher in Jinhua,with high resistance to beta-cypermethrin,medium resistance to deltamethrin(RR=8.87)and dichlorvos(RR=7.86),and low resistance to propoxur(RR=2.36)and acephate(RR=1.16).Conclusions B.germanica cockroaches in Zhejiang Province are highly resistant to pyrethroid insecticides,with certain resistance to other insecticides.Future control strategies should choose appropriate insecticides according to the resistance of B.germanica.