Changes in the population density,infestation rate,and insecticide resistance of Blattella germanica in Nanjing,China,2012-2022
Objective To investigate changes in the density,infestation rate,and insecticide resistance of Blattella germanica in Nanjing,China,so as to provide a theoretical basis for scientific and rational use of insecticides.Methods From 2012 to 2022,the density and infestation rate of B.germanica were monitored in the 12 districts of Nanjing,and the resistance of the samples to propoxur,beta-cypermethrin,deltamethrin,acephate,and chlorpyrifos was tested by using the residual film method.The data were processed using the Probit module of SPSS 22.0 software.Spearman's rank correlation analysis was conducted to correlate year with density,infestation rate,and resistance ratio.Results From 2012 to 2022,the densities of cockroaches were 1.01,1.62,2.17,1.36,1.21,0.77,0.58,0.39,0.39,0.29,and 0.24 individuals/trap,respectively;and the infestation rates were 20.79%,28.80%,32.45%,28.89%,17.31%,10.92%,6.73%,5.64%,4.67%,5.00%,and 3.36%,respectively.The density and infestation rate reached their peaks both in 2014,and decline since 2015,showing significant negative correlations between the year of investigation and the density and infestation rate(ρ=-0.897,P<0.001;ρ=-0.909,P<0.001).Propoxur resistance commenced at a low level in 2015,and the resistance ratio peaked at 4.73 in 2020,showing a significant positive correlation between the year and the resistance ratio(ρ=0.929,P=0.003).Beta-cypermethrin resistance increased to a medium to high level since 2015,and the resistance ratio reached the peak of 40.53 in 2020,showing a significant positive correlation between the year and the resistance ratio(ρ=0.821,P=0.023).Deltamethrin resistance increased to medium to high or even to extremely high levels since 2015,with no significant correlation between the year and the resistance ratio(ρ=0.714,P=0.111).The levels of resistance to chlorpyrifos and acephate were low in general,with no significant correlation between the year and the resistance ratio(ρ=-0.003,P=0.624;ρ=-0.771,P=0.072).Conclusions From 2012 to 2022,the density and infestation rate of B.germanica in Nanjing showed a downward trend,while the resistance to propoxur and beta-cypermethrin increased.The increasing resistance of B.germanica may lead to a rebound in its density and infestation rate,which should be paid more attention to.
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