| Athetis lepigone(M?schler) is a new corn insect pest as the farming system has changed in recent years. The occurrence region of A. lepigone has been expanding since it was firstly observed injured summer corn seedling in 2005 in Hebei province.. It has become one of the important insect pests at summer corn seedling stage in Huang-Huai-Hai Region. A. lepigone is a polyphagous insect, which can feed on a variety of vegetables and crops, weeds and even decayed plant debris. It has 4 generations a year, the second generation larvae usually cause the most serious damage to summer corn seedlings, the other generations rarely damage crops.The genetic structure of A. lepigone collected from 15 geographic locations from 5 provinces in North China was analyzed using ISSR molecular markers, the genetic differentiation among populations and gene flow were also tested.Wolbachia infection status of collected populations was studied, the infection rate and strain were determined, the phylogenetic tree was constructed based on COI gene sequences. The effects of Wolbachia on mt DNA variation and evolution in natural populations of A. lepigone were evaluated. The host plant sources of three generations adults collected from Shijiazhuang of Hebei, Dezhou of Shandong, Xuzhou of Jiangsu were analyzed using stable carbon isotope technique. The primary achievements of this dissertation are listed as follows:Inter-simple sequence repeat(ISSR) markers were used to determine genotype of A. lepigone collected from 15 geographic locations in North China. Data from seven primers resulted in a total of 183 bands that were scored, 174(95.08%) of which were polymorphic. Genetic distance estimates among the 15 populations of A. lepigone ranged from 0.0133 to 0.0595. At species level, Nei’s genetic diversity index was 0.3537 and Shannon information index was 0.5288. Genetic differentiation was estimated at 0.0747 and historical mean number of migrants(Nm) was 6.19. Clustering and mantel analysis revealed no correlation between genetic diversity and geographic proximity among the A. lepigone populations. This lack of significant genetic diversity or correlation with geographic location suggests that gene flow may be high among the populations or homogenization may be a result of recent range expansion.The effects of Wolbachia infection on mt DNA variation was studied on A. lepigone larvae in 12 geographical populations from North China. Mitochondrial COI gene and Wolbachia wsp gene were both obtained from 423 individuals, infection rate was 9.3%, ranged from 0 to 26.19%. Wolbachia types were divided into three strains, named w Lep1, w Lep2, and w Lep3(KJ596655-KJ596657), respectively. The haploid network graph showed that mt DNA haploid type and Wolbachia infection had no obvious relationship. For each infected population, the correlation analysis results of haplotype and nucleotide diversity index with Wolbachia infection rate indicated that the Wolbachia infection had no obvious effect on mitochondrial genetic evolution. AMOVA analysis showed that genetic variation mainly exists within populations, but the proportion of variation within populations in uninfected individuals is lower than that in infected individuals.The movement among A. lepigone host plants of different generations in different locations were studied. Four generations of A. lepigone adults were collected from three different localities including Shijiazhuang of Hebei, Dezhou of Shandong, Xuzhou of Jiangsu, form June 2013 to September 2014. The δ13C values of the wings of each tested moths collected from overwintering, first, second, third generations were measured which could indicate the larval host plant photosynthetic pathway(C3/C4). The results from two years were basically consistent. Overwintering generation larval host plants were mostly from C3 plants, partly(20%~30%) were from C4 plants; first and second generations larval host plants were all basically from C3 plants. Most of host plants of the third generation larvae were from C4 plants, some(20%~40%) were from C3 plants. |
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