| The supercooling points in different stages, the abilities of cold hardiness and overwintering of pupae in diamondback moth, plutella xylostella(L.)(Lepidoptera:Plutellidae), have been studied. And the mtDNA COI sequence from 10 geographic populations of p. xylostella Beijing, Shanghai, Guangdong, Hunan, Zhejiang, Heilongjiang, Gansu, Yunnan, Hainan and Shandong population were investegated in this thesis. The main results obtained are showed as follows:(1) The results showed that the supercooling abilities varied significantly in different developmental stages of p. xylostella. The supercooling point was the lowest with -20.12℃in pupae, the next was adult with -16.56℃, and higher in larvae with -13.72℃in average. The supercooling point in the 4th instar larvae was the highest (-8.5℃), suggesting that the cold tolerance of pupae was the greatest and most possible stage to overwinter.(2) The time of 50%, 90% and 99.9% lethality (LT50 ,LT90 ,LT99.9) in pupae shortened with the temperature decreasing. Under - 10℃- 5℃, 0℃and 5℃, the LT99.9 was 10.29d, 21.68d, 27.77d and 41.39d respectively, showing the p. xylostella can't pass the winter where the temperature is below 0℃for more than 28 days. The results from pupae burying experiments in different 4 areas in Beijing for two years showed that the overwintering mortality were 100%. In the overwintering experiment in open field, there was no adult survived in the soil collected in early spring. It was concluded that p. xylostella couldn't pass the winter in the open field in Beijing, from the analysis in combination with the Beijing climatic data.(3) The length of the mtCOI gene fragment amplified was 266 bp, and the sequences of 60 samples were detected. Through comparison, 2～27 variable sites in each population were found, among which 0～21 parsimony-informative sites were existed. The mean content of A+T was ranged from 70.5% to 71.7%. Among the COI gene of different populations of p. xylostella, the diversity sites, haplotype diversity (Hd), nucleotide diversity, average number of nucleotide differences (k) were 34, 0.892, 0.01832, 4.872 respectively. The value of Tajima's D was -1.90230 (P < 0.05), and the test were significant, It was concluded that mtDNA evolution does not followed neutral models, suggesting that the results of sequence evolution was not random genetic drift of the natural populations. The value of Fu's Fs test was all negative, so the population of p. xylostella was likely to expand in the past.(4) The genetic distance was among 0.008~0.095 of the COI gene of experiment populations. The evolutionary distance was close with the value of 0.008 between the Beijing and Guangdong, Hunan, Yunnan and Zhejiang population, while it was far between Beijing and Gansu populations with the value of 0.051. The genetic distance was the farthest between Shanghai and Beijing, Guangdong, Yunnan, Zhejiang populations with the value of 0.095. The AMOVA analysis of the Fst and the average pairwise differences among 10 geographic populations of p. xylostella showed that significant genetic diversities were found between Beijing and Shanghai, Guangdong, Shandong populations. In the meantime, genetic differences were found between Shanghai and the other 8 populations except Shandong population. Analysed from comparison of the data above, Beijing populations of p. xylostella have the smallest genetic difference with Hunan, Hainan populations, and the greatest difference with Shanghai population.(5) In the 60 samples analysed, 24 haplotypes were found. The haplotype accounted for 40 percent of all individuals. Only eight haplotypes were shared by at least two individuals. Eight populations had their unique haplotypes, which showed that there was some genetic difference among the geographical populations. However the genetic diversity was low concluded from the NJ phylogentic tree.From the above results, it is suggested that 1) p. xylostella couldn't pass the winter in the open field in Beijing, and the moths in the original appearance in spring were migrated from other area, except from greenhouses; 2) there was close relationship between Beijing population and other populations of p. xylostella. High frenquency for gene flow was existed and the source of immigrated moth was from many areas.
|
PDF Full Text Request