Studies On The Sensitivity To Insecticides In Meteorus Pulchricornis And Regulation Of MiRNAs Expression In Spodoptera Litura By Parasitoid Wasp

Meteorus pulchricornis,a solitary endoparasitoid,is the parasitic natural enemy of maior lepidoptera pests,such as Spodoptera litura,Helicoverpa armigera and Lymantria dispar.However,in mulberry field ecosystem,the life history characteristics of M.pulchricornis against commonly used insecticides is unclear.The purpose of this study was to elucidate the immune response regulation process in S.litura response to the parasitism of M.pulchricornis.Therefore,this study explores the fitness characteristics and detoxification mechanisms in M.pulchricornis against cypermethrin and phoxim,and reveals the physiological change mechanism of S.litura response to M.pulchricornis from the regulation of miRNAs on host immune.It was elucidated the molecular mechanism of parasitoid wasps under insecticide stress and regulating host physiological process,in order to provide a reference for fully developing the control potential of parasitoid wasps in integrated pest control in mulberry field ecosystem.The main results are as follows:?1?The toxicity results determined by dropping method showed that the theoretical LC₅₀values were 4.608 and 8.570 mg/L after exposure to phoxim and cypermethrin for M.pulchricornis adult for 24 h,respectively.LC₅₀ dose of phoxim significantly reduced the number of cocoons,cocoon weight,emergence rate and hind tibia length of M.pulchricornis offspring.Phoxim at LC₃₀ dose significantly reduced the number of cocoons,cocoon weight,and longevity of parasitoid offspring.While cypermethrin at LC₃₀ and LC₅₀ doses significantly prolonged the development time from cocoon to adult of parasitoid offspring,and there were no significant effect on other fitness indicators.These results showed that the two insecticides had sublethal effect on M.pulchricornis.?2?A total of 17 glutathione s-transferase genes?Mpul GSTs?,including 15 cytosolic GSTs and 2 microsomal GSTs,were identified from the body transcriptome of M.pulchricornis.The 15 cytosolic GSTs were classifed into four classes:four in Delta,three in Omega,seven in Sigma,and one in Zeta.The activities of detoxification enzymes in M.pulchricornis were significantly affected by phoxim and cypermethrin at LC₃₀ dose.The results of q RT-PCR showed that 7 Mpul GSTs and 11 Mpul GSTs were upregulated at the sublethal doses of phoxim and cypermethrin,suggesting that these Mpul GSTs might be involved in the detoxification of organophosphorus and pyrethroid insecticides.?3?In this study,small RNA libraries of S.litura parasitized by M.pulchricornis and unparasitized host were constructed.A total of 133 miRNAs were identified from two s RNA libraries,including 80 known and 53 new miRNAs,and their target genes were predicted and annotated.There were 66 miRNAs significantly differentially expressed in the two s RNA libraries,among which 36 miRNAs were significantly up-regulated and 30 miRNAs were significantly down-regulated.The results indicated that the parasitism of M.pulchricornis could cause the change of miRNAs expression in S.litura.?4?29 miRNAs of S.litura that were significantly up-regulated after parasitization at different time.Immune-related Sli-miR-2a-3p,Sli-miR-10464-5p and Sli-miR-34-5p were randomly selected for subsequent functional verification.The results of q RT-PCR and double luciferase reporter assay showed that these miRNAs could bind to CDS sequences of antimicrobial peptide,3'UTR sequences of Atlastin and Ftz-F1 to regulate the expression of their target genes,respectively.Up-regulation of Sli-miR-34-5p expression after parasitization could increase the cocooning rate of M.pulchricornis and prolong their longevity,while down-regulation of Sli-miR-34-5p expression could reduce the cocooning rate of parasitoid wasp.The results showed that M.pulchricornis could regulate Sli-miR-34-5p expression in the host to facilitate to achieve higher fitness for parasitoid wasp progeny.