| Monochamus alternatus Hope,as the main transmission medium of pine wilt disease,effectively controlling M.alternatus has become the key link to curb the spread of pine wilt disease.Changes and fragmentation of species habitat landscape pattern are the main reasons threatening biodiversity and species survival.At the same time,the outbreak of pests and the heredity among pest populations are also closely related to landscape pattern.The study on the combination of pests and landscape pattern is helpful to the development of sustainable pest management countermeasures.Although previous studies have described the relationship between landscape patterns and Monochamus insects,they mostly focused on climate,altitude and other environmental factors.However,there was no comprehensive study on the population dynamics and genetic diversity of M.alternatus in heterogeneous landscape patterns,especially the relationship between the detailed forest landscape and non-host landscapes such as cities,farmland and roads.This information is particularly important to clarify the dispersal behavior of M.alternatus in a heterogeneous landscape,as well as to efficiently controlling.Therefore,this study combined landscape ecology and landscape genetics,discussed the impact of landscape pattern on the population density of this insect,and studied its relationship between genetic diversity and different landscape scales and landscape types by whole-genome resequencing and model construction.It will be of great significance to explain the disaster mechanism of pine wood nematode disease and make effective prevention and control measures by using landscape pattern.The main research results are summarized as follows:1.Effect of landscape pattern on population density of M.alternatusIn order to explore the relationship between landscape pattern and population density and adult occurrence period of M.alternatus,the correlation between patch type and landscape index at two levels of landscape and population density and adults occurrence period was analyzed based on the research method of landscape ecology,The results showed that the patch area of forest and the number of road patches were significantly positively correlated with its population density,while the division of road patches and the patch area of farmland were significantly negatively correlated with the population density of this species.Landscape indices such as patch density of forest land and roads,urban,farmland and waters have an important impact on the adults occurrence period.2.Genetic diversity of M.alternatus population at different landscape scalesTo clarify the genetic diversity of pine longicom beetle population under landscape pattern,the genetic diversity and population structure of M.alternatus population under different scales were analyzed by whole-genome resequencing.The results showed that there were significant differences in the population structure of M.alternatus at different landscape scales.Among the study areas of Shunchang and Xiapu were obviously separated from each other in phylogenetic tree,PCA and ADMIXTURE analysis,belonging to different populations.This indicated that there were significant obstacles in natural spread and gene communication of the pine longicom beetle populations at larger scale(>250 km)in the county.However,within a fine scale(<10 km),the genetic structure difference of this insect population in the two study areas was weak,but it has certain influence,in which the expected heterozygosity(H_E)in Shunchang county was 0.2208-0.2383,the allele richness(A)was 0.7613-0.7752,the expected heterozygosity in Xiapu county was 0.2015-0.2127,and the allele richness was 0.7754-0.7674.3.Effect of landscape pattern on genetic diversity of M.alternatuIn the analysis of the influence of landscape pattern on the population density of M.alternatus and the genetic diversity at different landscape scales,it was found that landscape pattern was related to both.If the influence of different landscape elements in landscape pattern on the this speices genetic diversity can be further explored,it will be helpful to understand its spreading behavior in landscape pattern and formulate effective prevention and control measures.Therefore,the least-cost path,LCTA,MLPE,db-RDA and other models were used to analyze the impact of landscape pattern on the genetic diversity of pine sawyer population.This study found that in a small scale(< 10 km),the correlation between geographic distance and its genetic distance was not significant,while the landscape distance under the path of least-cost had significant effect on genetic distance.By analyzing the effects of different landscape types on gene flow and genetic diversity of M.alternatus,it is found that the host forest landscape(P.massoniana,P.elliottii,Mixed forest containing host)was a habitat that promotes the species diffusion,and was positively correlated with genetic diversity,while the non-host forest(C.lanceolata)was negatively correlated with gene flow.Different man-made landscapes had different effects,among which the road landscape wss correlated with its gene flow and genetic diversity,proving that human-mediated behaviors such as wood transportation could promote the spread of M.alternatus,but farmland and city had negative effects. |
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