| Insects are organic components of forest ecosystem. While under biotic and abioticdisturbance or functional degradation and disorder of forest ecosystem, the related controllingfactor would lose the balance and population density, and structure and spatial pattern wouldchange, which makes forest ecosystem lose the control and eventually lead to the outbreak andprevalence of insects. Therefore, unraveling the occurrence mechanism of forest diseases andinsect pests, understanding formation process and reasons of the forest pest disasters willprovide scientific basis for utilizing biodiversity and ecosystem structure of natural forest toself-regulate its diseases and pests disaster, improving forest pest Ecological Pest Managementtheory and achieving sustainable control of harmful forest organism.This thesis identifies Cephalcia kunyushanica in Pinus densiflora ecosystem of KunyuMountains as the research subject, and bases on the statistics on plants and insects of40permanent plots as well as statistics on arbor of a2hm2plot. By studying the impacts of sitefactor, stand structure, tree species composition, neighbor tree of host, plants and insectdiversity on C. kunyushanica population of Kunyu Mountains, and building up structuralequation model, it reveals occurrence mechanism of C. kunyushanica population and complexdirect and indirect ecological relationship between its influencing factors. The results reveal:(1) Elevation, aspect and soil depth has no obvious correlation with C. kunyushanicapopulation. Slope has a significant positive correlation with density of C. kunyushanica(P<0.001), and it increases with a bigger gradient. In structural equation model, taking slope aslatent variable of observed variable, site factors have positive direct effects on plant diversityand have no significant effects on C. kunyushanica population. Site factors have indirect effectsand positive total effects on C. kunyushanica population through the co-effect of other factors.(2) C. kunyushanica population has no significant correlation with stand density, standsage, canopy, and herbaceous coverage and is significantly positive correlated with P. densiflora percentage and shrub coverage, which suggests C. kunyushanica population has a biggerdensity with a higher P. densiflora percentage and shrub coverage. Stand structure, latentvariable of structural equation model, is observed by P. densiflora percentage and shrubcoverage as the observed variable. The result shows stand structure has a relatively significantpositive correlation with both P. densiflora percentage and shrub coverage. Stand structure hasdirect effects on C. kunyushanica population, and has no significant direct effects on plantsdiversity and insect diversity, through the co-effective of which, stand structure has negativeindirect effects on C. kunyushanica population diversity.(3) Larval density of C. kunyushanica is significantly positive correlated with speciesrichness and diversity of trees and shrub, and has no significant correlation with speciesrichness and diversity of herbaceous plants. Plants diversity, as latent variable observed bytrees, shrub and herbaceous richness in the structural equation model, has significant positiveeffects on C. kunyushanica population. Species richness of trees and shrub is significantlypositive correlated with plant diversity, and with less correlated with herb richness. Plantdiversity is significantly positive direct effected by stand factors and less directly affected byforest types and stand structure, and has a weak and insignificant negative direct effects oninsect diversity.(4)72328insect specimen, in603species or morphospecies,133families and15orders,was collected from litter, understory and crown canopy layer of40plots. Species accumulationcurve analysis shows Jackknife1acquires a expecting species density of795(±34), expectingspecies density of actual observed species accounting for75.8%of the whole species.50.2%ofthe total insects were collected from Litter layer, with259species.28468insects werecollected from understory layer, taking up91.5%of the total species.88families and246species of insects were collected from crown canopy layer occupying10.5%of the total insectamount. C. kunyushanica community is significantly net associated with interspecificassociation, and C. kunyushanica population is significantly positive associated with fourspecies and significantly negative associated with seven species. (5) Richness, abundance and diversity index of insects population in Kunyu Mountains isnot significantly correlated with population density of C. kunyushanica, which is onlysignificantly negative correlated with litter layer insects species and diversity index (Pn=0.023;Ps=0.035) and is not correlated with understory and crown canopy layer. The amount of C.kunyushanica population has no significant correlation with richness, abundance andShannon-Weiner diversity index of predates and parasitism natural enemy insects, and hassignificant positive correlation with richness and abundance of phytophagous insects. Twocommunity stability index, richness and abundance ratio and abundance ratio of natural enemyand phytophagous insects, have no significant correlation with the amount of C. kunyushanicapopulation. It suggests the amount of C. kunyushanica population is not quite affected byinsects community stability. In structural equation model, insect diversity has no significantpositive direct effect on C. kunyushanica population.(6) Plant associational effect on C. kunyushanica population was observed on three scales,nearest neighboring tree of host,―1+4‖spatial structural unit of the nearest four tree and thehost and the stand. Nearest neighboring tree of host has a bigger effects if it is P. densiflora,while has on obvious influence as other species. One or more P. densiflora in―1+4‖spatialstructural unit makes no great change in C. kunyushanica population density, while no P.densiflora in―1+4‖spatial structural unit would push C. kunyushanica to focus on the host, P.densiflora, which may easily cause associational susceptibility. P. densiflora in nearestneighboring is positively related with density of C. kunyushanica population. In the stand scale,the more the C. kunyushanica nearest to phylogenetic relatedness, where trees tend to form theforest, the bigger the coefficient of variation is, and it‘s likely it form a associationalsusceptibility. The mixed forests tend to be associational resistance while it is farther fromgrowth system (Family, Order, and Class). In structural equation model forest type, as latentvariable, directly negative associated with C. kunyushanica population and co-effected throughsome other factor. (7) In this thesis, structural equation model was built up based on latent variable standfactor, forest type, and stand structure as well as plants and insects diversity. It has thegoodness of fit and can explain more than65%of the variable of C. kunyushanica population.Structural equation model reveals that plant diversity (positive effect) is the most importantdirect factor on the amount of C. kunyushanica population, with stand structure (positive effect)and forest type (negative effect) ranked the second. Stand factor positively influence C.kunyushanica population on the whole. Structural equation model without insects diversity aslatent variable, AIC (Akaike Information Criteria) and CAIC (Consistent Akaike InformationCriteria), has an average smaller than the model with insects diversity, could excellentlypredict and explain occurrence mechanism of C. kunyushanica. |
