Mixed-population Dynamic Of Boring Insect And Environmental Effects In Artemisia Ordosica Shrubs

Artemisia ordosica is exclusively distributed in temperate and semi-arid sandy deserts of north China.It plays important roles in sand fixation and vegetation restoration.Nowadays,A. ordosica borer insects:Adosopius sp.(Coleoptera:curculionidae),Holcocerus artemisiae(Lepidoptera:Cossidae),Sphenoptera sp.(Coleoptera:Buprestidae) and a Tortricidae species are outbreaking and causing large area death of A.ordosica in Inner Mongolia,Ningxia, Shaanxi,and Gansu provinces etc.A.ordosica borer insect abundance and environmental effects were studied and the results showed as follows.1.61 plots damaged by boring insects were taken as an example at different successional stages of A.ordosica community in Ningxia.A predictive model of percent of trees with the boring insects is established by linear stepwise regression analysis,using population densities of Sphenoptera sp.(Family:Buprestidae),crust type,population densities of Holcocerus artemisiae (Family:Cossidae) and A.ordosica age as parameters.Actual inspection shows that this model has good prediction function which can be applied in practice of forest pest control.2.In order to understand the relationship between occurrence of the boring insects and environment effects,during May,2006 to September,2007 a systematic survey was conducted under 3 different successional stages of A.ordosica that is located Yanchi in Ningxia Hui Autonomous region,China.The result shows that the boring insects have the ability to bore the A. ordosica at 3 different successional stages of A.ordosica,but the dominant species are different at every successional stage.A predictive model of boring insects population densities is established by linear stepwise regression analysis.The predictive model indicated that the environment factors have significantly influence on the population densities of A.ordosica boring insects.3.Nowadays,large amount A.ordosica were found dead when they grew up to a certain age. The damage from A.ordosica boring insects is one reason.Systemic research of A.ordosica damaged by these boring insects were investigated in Yanchi County,Ningxia from April to August during 2007～2008.The result showed that 42.22%A.ordosica were attacked in all 848 plants investigated,which had 361 Sphenoptera sp.accounted for 62.35%,105 Adosopius sp. accounted for 18.13%,69 Holcocerus artemisiae accounted for 11.92%and 44 Tortricidae stem pests accounted for 7.60%.Ages and ground diameters of A.ordosica were closely related to pest densities of the mixed pest populations based on this study.4.The investigation on the spatial patterns of A.ordosica boring insects(ABI) larvae, parasitoid Pyemotes herfsi Oudemans and ABI-preying Perdix dauuricae pecks in A.ordosica community showed that in horizontal direction,ABI larvae,parasitoid Pyemotes herfsi and Perdix dauuricae pecks were in negative binomial distribution,while in vertical direction,ABI larvae were distributed on A.ordosica from above ground 6cm to under ground 12cm in height,with a peak around the 3cm～6cm,Their natural enemies also favored this range.