Studies On The Variance In Sensitivity Of Different Lines Of Spodoptera Litura To Insecticidal Microorganisms

Genetic variation in host populations is very important for the defense against parasites,and it has been confirmed in both vertebrate and invertebrate.Spodoptera litura(Fabricius)belongs to Lepidoptera,Noctuidae,and it is a polyphagous pest of many agricultural crops,and occurs all over the world.Bacteria,fungus and virus are all important pathogens against S.litura,we know little about the variance in susceptibility to the microorganisms among different lines of the pest.Serratia marcescens,Nomuraea rileyi and S.litura nucleopolyhedrovirus(SpltNPV)are common insecticidal microorganisms in nature,andthey all can infect S.litura.We have established three S.litura lines with genetic difference from Hexian,Anhui province,China.In this study,we compare the susceptibility of the three S.litura lines to Serratia marcescens,Nomuraea rileyi and SpltNPV,and we also investigate the infection of symbionts in the three S.litura lines,then we analyze the relationship between the variance in susceptibility among different lines and the infection of symbiont in the three S.litura lines.The main results are as follows:(1)Comparison of the fitness among the three S.litura lines:To clarify whether there is difference in the fitness among difference lines from the same population,the three S.litura lines from Hexian,Anhui were used to compare the fitness.Investigation on the development of the three S.litura lines from newly-hatched larvae to pupation indicated that there was no difference in developmental duration,pupation,sex ration,and there was only difference in the body weight of male pupae among the lines.(2)Variance in the susceptibility of the three S.litura lines to different insecticidal microorganisms:In order to know the differentiation in susceptibility to insect pathogens among the pest lines,comparison on the susceptibility of the three S.litura lines to Serratia marcescens,Nomuraea rileyi and SpltNPV was conducted,it was found that there was difference in the susceptibility of the three lines to the pathogens,and the difference among lines varied with the species of pathogens.Line B showed the highest susceptibility to Serratia marcescens,but the lowest susceptibility to Nomuraea rileyi and SpltNPV.The results suggested that,there was a trade-off in the susceptibility to different insecticidal microorganisms within the population of S.litura,and these was beneficial to improve their resistance to the pathogens.(3)Symbiont infection in the three S.litura lines and its association with the variance in susceptibility among lines:The presence of the four kinds of symbiotic bacteria including Cardinium,Arsenophons,Spiroplasma,Wolbachia were tested the three S.litura lines,and only Wolbachia could be detected in the lines.There was difference in the infection frequency of Wolbachia among the three lines,and the infection rate in line B was 20.5%which was the highest.Linking the susceptibility and the Wolbachia infection,we inferred that Wolbachia infection might play roles in mediating the resistance of S.litura to Nomuraea rileyi and SpltNPV.