Detection Of Susceptibility Of Diaphorina Citri To Two Insecticides And Analysis Of Endosymbiotic Bacteria

Diaphorina citri Kuwayama belongs to Hemiptera,Psyllidae,which mainly harms the genus Rutaceae.The insect not only causes direct damage to the host leaf by sucking it,but the most serious harm is the spread of citrus Huanglong disease,causing serious economic losses to the citrus industry.The prevention and control of citrus psyllid has been dominated by chemical control for a long time.In particular,neonicotinoid insecticides such as thiamethoxam and imidacloprid have been widely used in the control of citrus psyllid,making citrus psyllid have different degrees of resistance to such agents.At present,there are few reports on the mechanism of resistance of citrus psyllid to insecticides.In this study,collected three geographical populations of citrus psyllid from Guangzhou Xinfang,Zhangzhou Yongxing and Yongzhou Jiangyong were collected.The susceptibility of three citrus psyllid populations to thiamethoxam and imidacloprid was tested.The citrus psyllid resistance to imidacloprid was studied.The expression changes of five P450 genes in imidacloprid resistant strain and sensitive strain were studied,and 16S rDNA amplifier sequencing was used to analyze the species and content differences of symbiotic bacteria among three resistant and susceptible strains of citrus psyllid,which laid a foundation for further study on the resistance mechanism of citrus psyllid to neonicotinoid insecticides such as imidacloprid.1.Sensitivity of three different citrus psyllid populations to thiamethoxam and imidacloprid insecticidesSensitivity detection of neonicotinoid insecticides thiamethoxam and imidacloprid to three geographical populations of citrus psyllids in Guangzhou,Zhangzhou and Yongzhou by bioassay.The susceptibility of three citrus psylla populations to insecticides was quite different.The LC50 of Citrus Psylla populations in Chenzhou was 3.85 times higher than that in Guangzhou,and the susceptibility declined.The resistance to imidacloprid was 5.16 times,which was at a low level.The resistance to thiamethoxam and imidacloprid of citrus psylla in Yongzhou was 2.18 times and 2.66 times,which was in a sensitive state.From the results,the decrease of sensitivity to insecticides in different degrees of citrus psyllid indicated that there was a potential risk of developing resistance to insecticides in these areas.2.Relative expression of P450 gene in resistant and susceptible strains of Citrus Psylla in fieldIn this study,the expression levels of CYP4C67,CYP4C68,CYP4DA1,CYP4DB1 and CYP4G70 genes in five imidacloprid-resistant strains of Citrus Psylla in the field were up-regulated by fluorescence quantitative PCR.Five P450 genes were up-regulated after 12,24 and 48 hours of LC₅₀ imidacloprid treatment.After treatment for 12 hours,the relative expression of the five P450 genes was 4.27,1.77,1.47,1.20 and 1.36 times of the control group,respectively.After treatment for 24 hours,the relative expression of the five P450genes decreased gradually.After treatment for 48 hours,there was no significant difference in the relative expression of the other four P450 genes except CYP4C67 gene between the control group and the control group.3.Analysis of the difference of symbiotic bacteria among different resistance levels of Citrus Psylla speciesMicroorganisms in insects can induce the production of detoxifying enzymes,thus losing the toxicity of insecticides.In this study,16S rDNA macrogenome sequencing was used to analyze the symbiotic bacteria in three populations of Citrus Psylla species with different resistance levels:Guangzhou?G.a.1?relative sensitivity,Chenzhou?C.a.1?low level resistance and Yongzhou?Y.a.1?sensitive decline.The number of OTUs in species classification was 6110.The results showed that the microbial diversity among the sample groups was Chenzhou?C.a.1?>Yongzhou?Y.a.1?>Guangzhou?G.a.1?.The abundance of microorganisms in three samples at generic level was C.a.1>Y.a.1>G.a.1.In this study,the abundance of Staphylococcus,Lactobacillus,Cetobacterium,Thermobacillus and Acinetobacter in Chenzhou?C.a.1?was significantly higher than that in Guangzhou?G.a.1?and Yongzhou?Y.a.1?.The roles of these strains in insect resistance formation and whether they can degrade exogenous toxins need to be further studied in the future.