Resistance Monitoring And Mechanism On Sublethal Effect Of Sulfoxaflor In Sitobion Miscanthi (Takahashi)

Sitobion miscanthi,as one of the wheat insects in our country,causes economic losses seriously and restricts the production of wheat of Chinese grain industry every year.At present,the prevention and control of S.miscanthi in China is mainly based on chemical insecticides,the problem of resistance become serious because of long-term irrational use of insecticides.Sulfoxaflor,the first sulfoximine insecticide,has a unique insecticidal site which is widely used to control sap-sucking insects such as aphids.It is important to clarify the resistance level of sulfoxaflor and other commonly used insecticides with the metabolic detoxification mechanism of S.miscanthi by sulfoxaflor.Based on these,we monitored the susceptibility to different insecticides and the sublethal effect of sulfoxaflor,which revealed the formation mechanism of metabolic resistance of sulfoxaflor to S.miscanthi at the molecular level.Our study will establish theoretical foundation for formulating integrated control strategies of wheat aphids.The main research results are as follows:1.Resistance level in the field populations of S.miscanthi to different insecticides in ChinaThe immersion method was used to determine the susceptibility in the field populations of S.miscanthi from ten different provinces in China（2021）.The results showed that most of the field populations of S.miscanthi had different degrees of resistance to five commonly insecticides（sulfoxaflor,beta-cypermethrin,imidacloprid,avermectin,chlorpyrifos）.Among them,the field populations in Guiyang,Guizhou,Xiangyang,Hubei,Linfen,Shanxi,Yangling,Shaanxi and Kashi,Xinjiang of S.miscanthi produced moderate level of resistance to imidacloprid and sulfoxaflor.In addition,the field populations of S.miscanthi in Hefei Anhui,Xiangyang Hubei,Xinxiang Henan,Linfen Shanxi and Kashi Xinjiang also had moderate resistance level to avermectin.Futhermore,most of the populations were in low resistance level to beta-cypermethrin and chlorpyrifos.According to the correlation analysis of the toxicity by different insecticides to the field populations of S.miscanthi,the results showed that there was a significant correlation between imidacloprid and chlorpyrifos（P<0.01）.2.The influence of sublethal effect and detoxification enzymes on S.miscanthi induced by sulfoxaflorAge-stage two-sex life table was used to study the effect of development and fecundity on F₁ generation of S.miscanthi after treated with sublethal concentration of sulfoxaflor(LC₁₀).The results showed that the induction of sulfoxaflor significantly shortened the developmental duration of nymph(1^st-instar and 4^th-instar),the adult preoviposition period（APRP）and the total preoviposition period（TPRP）of S.miscanthi.In addition,according to age-stage survival rates(s_xj)curve and age-stage reproductive value(v_xj)curve,the reproduction ability and survival rate decreased significantly under the treatment of sulfoxaflor,which indicated that sulfoxaflor had an adverse effect on the future development of S.miscanthi.According to the synergistic experiment of enzyme inhibitor on S.miscanthi,the results showed that the co-processing of piperonyl butoxide（PBO）and sulfoxaflor had sustained synergistic effect on S.miscanthi,suggesting that the activities of cytochrome P450 enzyme might play a major role in the metabolic regulation mechanism of S.miscanthi on sulfoxaflor.3.Identification and functional verification of P450 gene related to metabolism of S.miscanthi induced by sulfoxaflorThe results of transcriptome sequencing showed that the relative expression level of 328 genes in S.miscanthi was significantly changed after the treatment with the sublethal concentration of sulfoxaflor(LC₃₀),of which 273 genes were significantly up-regulated and 55 genes were significantly down-regulated.The GO and KEGG enrichment analysis showed that some differential genes were annotated to metabolic pathways,drug detoxification and cytochrome P450 pathways.The genes that related to detoxification metabolism were screened from transcriptome data,including four UDP-glycosyltransferase genes,eight P450 enzyme genes and two ABC transporter genes.The m RNA expression level of the detoxification enzyme genes was analysed by qRT-PCR and the full-length sequence cloning revealed that the expression level of the CYP6A13 increase significantly 1.35-fold（P<0.01）.RNAi was carried out by nano materials with topical application method,and the results showed that the susceptibility of S.miscanthi was restored after CYP6A13 was silenced under the treatment of sulfoxaflor,which confirmed that the up-regulated expression of CYP6A13 played an important role in the metabolism and resistance evolution formation of S.miscanthi.