Adaptability Of Spodoptera Litura Nucleopolyhedrovirus To The Genetic Diversity Within Host Population

Genetic variation in host populations is very important for the defense against parasites, and it has been confirmed in both vertebrate and invertebrate. Nucleopolyhedrovirus is a valuable resource for biological control of insect pests, and its adaptability to genetic diversity of host has rarely been studied. Spodoptera litura is a serious insect pest with broad host plant ranges, and it occurs in many regions and often causes heavy damage to vegetables and crops. S.litura nucleopolyhedrovirus (SpltNPV) is a natural regulator of the host and has been explored as insecticide to control the pests. What does variation in the genetic level of host within population look like? and how does NPV adapt to the genetic diversity of the host? Clarification of the above questions not only benefits to enrich the theory on coevolution of host and parasites, but also benefits the effective usage of NPV. Therefore, in the present study, we collected both the host (S. litura) and the parasite (SpltNPV) in the same location (Hexian, Anhui province, China), and investigated the genetic diversity of SpltNPV and S. litura, then we studied the adaptability of NPV to the genetic diversity of the host. The results are as follows:1 SpltNPV were collected from naturally-infected S.litura in Hexian, Anhui province, China, genotypes of NPV were isolated by in vivo cloning method,15 samples of SpltNPV were obtained with low lethal rate. Restriction endonuclease analysis of NPV genomic DNA of the above 15 samples indicated that no obvious difference was found in restriction enzyme profiles digested with EcoR Ⅰ, Hind Ⅲ or Pst Ⅰ enemyze. In order to detect the genetic difference among the 15 samples of NPV, we further amplified 7 types of genes including inhibitor of apoptosis protein (IAP),late expression factor lef-4, lef-5, lef-8, lef-11, p49 and helicase gene, and no difference in the sequence was found among the 15 samples in all the 7 genes. The gene sequence alignment results showed that sequences of genes from SpltNPV Hexian isolate were highly similar to the genes from other SpltNPV isolates. No genetic difference was found in SpltNPV Hexian isolate.2 We also collected S. litura in Hexian, Anhui province, and established 7 isofemales and continually reared them in the laboratory. To investigate the genetic difference of S. litura within population by AFLP (Amplified fragment length polymorphism) analysis, firstly, we used 4 pairs of primers to amplify the individulas from the 7 isofemales to preliminarily select the isofemales with obvious genetic difference. And then, we used 36 pairs of primers to amplify 45 individulas from 3 isofemales (15 individuals per isofemale). We obtained 1024 amplified fragments, the number of polymorphic bands was 880, the average number for each primer was 28.44. The average rato of polymorphism bands (PPB) is 86, Shannon’s diversity index was 0.4663, and the effective number of alleles ranged from 1.3816 to 1.7344. The 3 isofemales were genetically different, and the genetic differentiation between isofemale B and A or C was greater than that between A and C. The results indicated that there was genetic variance within S. litura Hexian population.3 Based on the establishment of S. litura isofemales with genetic difference and the isolation of SpltNPV which were all from Hexian, Anhui province, we further tested the pathogenicity of 6 samples of SpltNPV to the 3 isofemales. We found that there were significant differences in the pathogenicity of NPV on the different isofemales, and NPV showed the lowest activity to isofemale B which had greater genetic difference with isofemale A and C, and the highest activity to isofemale A, and the difference was consistent in the 6 samples of SpltNPV. Compared to the difference in pathogenicity, the difference in killing speed of NPV to different isofemales was less, among 6 samples of SpltNPV, only 3 of them showed difference in killing speed on different isofemales, and killing speed on isofemale B was more slowly than that on the other two isofemales. The results indicated that NPV could adapt to the host population with genetic diversity by infecting them with different levels.