Effects Of Juvenile Hormones And Molting Hormone On Immune Response Of Mythimna Separata (Walker)

The Mythimna separata（Walker）is an important agricultural pest that belongs to the Lepidoptera Noctuidae.In recent years,M.separata has frequently erupted in some areas of China,posing a major threat to food security.In previous work,we discovered that the M.separata larvae that caused outbreaks often underwent melanization,and the increased immunity of this melanized population was one of the important reasons for increased harm.However,whether this immunity was affected by endocrine hormones remained unclear.In this study,we measured the dynamic changes of juvenile hormone（JH）and molting hormone（MH）in M.separata larvae that treated with Beauveria bassiana,and clarified the influence of immune response to hormone.Furthermore,we injected juvenile hormone analogue（JHA）and 20-Hydroxyecdysone（20E）into M.separata larvae,and measure the influence of hormone on insect immunity.Our study would reveal the regulation mechanism of endocrine hormones on insect immunity,and provide a theoretical basis for M.separata control.The study clarified the effect of the M.separata immune response on the dynamic changes of JH and MH:Through the measurement of changes in JH and MH titers during the immune response of M.separata infected by B.bassiana,the contents of JH at 8,24,48 and 96h after the infection were significantly lower than that of the control（P<0.05）.However,the MH content of the 6^thinstar larvae of M.separata was significantly higher than that of the control at 8,72 and 96h after B.bassiana treatment（P<0.05）.These results indicated that JH and MH were closely associated with the immune response of M.separata.The immune response inhibited the accumulation of larvae JH,but promoted the accumulation of MH.The study confirmed that endocrine hormones have a significant regulatory effect on the immune response of M.separata:By injecting JHA and 20E to the 6^thinstar larvae of M.separata,the resistance of M.separata to B.bassiana and its related immunity were determined.The results showed that after being induced by JHA,the 6^thinstar larvae of M.separata infected by B.bassiana showed an upward trend in corrected mortality(F_5.12=3.170,P>0.05),but downward trend in pupation rate(F_6.14=2.847,P>0.05)and the feathering rate(F_6.14=3.686,P<0.05).However,no statistical significant difference was found.The main reason is that the JHA significantly reduces the relevant indicators of immune response in the body.After injection of JHA,the immune indexes such as the number of cell nodules,protein content,lysozyme activity,PO activity and antimicrobial peptide content in the larvae were all lower than that of the control group,and the differences were mostly significant 8-48h after infection（P<0.05）.Upon 20E induction,the infected mortality of larvae was significantly lower than that of the control(F_5.12=2.909,P<0.05).The immune indexes such as nodule number,protein content,lysozyme activity,PO activity and antibacterial peptide content in M.separata were significantly higher than those in the control group 8-48h after infection（P<0.05）.This shows that a certain concentration of JH is not conducive to the immune response of the M.separata larvae to Beauveria bassiana,while MH is beneficial to improve its immunity,and thus has an important regulatory effect on the immune response of M.separata.