Preliminary Study On The Toxicity And Resistance-related Genes Of TVM On Ae.aegypti

Aedes aegypti is one of the main mosquito vectors of insect borne diseases.Female mosquitoes transmit dengue,chikungunya,Zika and yellow fever viruses,which are pathoges seriously endangering human health.At present,mosquito management mainly involves environmental,physical,chemical and biological prevention and control,which mainly relies on chemical preventions and controls.However,chemical control,i.e.using pesticides,is a major tool in mosquito management,which has high efficiency,simplicity and broad spectrum in terms of mosquito species.The common used pesticides are pyrethroids,carbamates,organic phosphorus compounds,organic chlorine insecticides and macrocyclic lactones.However,excessive and improper use of insecticides leads to serious insecticide resistance,which requires to discover new pesticides to replace the old ones.Tenvermectin（TVM）is a new type of 16-membered macrolide insecticide.Studies have shown that TVM has high activity against the insects,Plutella xylostella,Helicoverpa armigera Hübner,Tetranychus cinnabarinus,Panonychus citri and other pests.In order to understand its toxicity,the following studies were carried out:1.Toxicity of TVM to three mosquito speciesIn order to study the effect of TVM on mosquitoes,the larvae of Ae.aegypti,Ae.albopictus and Culex pipiens quinquefasciatus were used in the bioassays.After 24hours of treatment with various concentrations of TVM,the LC₅₀ values of TVM to Ae.aegypti,Ae.albopictus and C.pipiens quinquefasciatus were obtained and they were2.181,0.589 and 0.139mg/L,respectively.The adults of Ae.aegypti were fed with sugar water containing different concentrations of TVM for 24 hours,and the survival rates within one week were counted.On the seventh day,the survival rates of control group and 0.1,1,2,5,10 ppm TVM treated groups were 93.33%,80.00%,66.67%,23.33%,3.33%and 3.33%,respectively.The results showed that TVM had better insecticidal activity to mosquitoes.2.Effect of TVM on fecundity of female Aedes aegyptiThe female Ae.aegypti mosquitoes were fed with the blood of mice injected with different doses of TVM.In three days after blood meal,they laid eggs on a white wet paper put into the mosquito cage.The number of eggs laid and hatched were counted.Compared with the control group,the egg production and hatching rate of 0.5 and 1mg/kg dose groups decreased significantly,the average numbers of egg production per one female of control,0.5 and 1 mg/kg TVM treated groups were 91.65,40.17 and38.54,respectively,and the hatching rates were 78.65%,40.60%and 34.92%,respectively.The results showed that TVM was able to reduce the reproduction of Ae.aegypti.3.Transcriptome analysis of Ae.aegypti larvae treated with TVMIn 24 hours treated of the treatment with TVM,the RNAS of Ae.aegypti larvae ware extracted and sequenced.The results showed that,compared with the control group,there were 2647 genes with significant difference in expression in the larvae of Ae.aegypti treated with TVM,of which 697 genes were up-regulated and 1950 genes were down-regulated.Six genes were randomly selected and verified by Real-time Quantitative PCR.The results were consistent with RNA seq results.Gene ontology analysis showed that differentially expressed genes were annotated into the following groups:cellular process,metabolic process,membrane,binding and catalytic activity.The differential gene KEGG Pathway is mainly enriched in drug metabolism,immune response,biosynthesis,digestion and absorption.4.Study on the genes potentially involved TVM resistance of Ae.aegyptiThe RNAi technology was used to interfere with GST-1 and Glu Cl,which were previously considered as macrolide insecticide resistance genes.The larvae of Ae.aegypti were fed with the bacteria expressing the target gene ds RNAs.The results showed that the relative expression of GST-1 and Glu Cl in the RNAi treated larvae decreased by 65.48%and 39.88%respectively compared with the control group.The LC₅₀ of GST-1 gene interfered mosquitoes was 1.292mg/L,and that of Glu Cl gene interfered mosquitoes was 2.371mg/L.In this study,it was found that TVM has a good insecticidal activity on mosquitoes.Feeding TVM via the blood meal affected the reproduction of female Ae.aegypti.It was preliminarily concluded that the interference of GST-1 would enhance the effect of TVM on the larvae of Ae.aegypti.This study provided a reference for an alternative mosquito control tool,potential macrolide pesticide resistance genes and insight into further study on the toxicological mechanism of TVM in Ae.aegypti.