Study On The Effect Of Desert Landscape Pattern On The Trophic Level And Population Viability Of Seed Pests And Its Natural Enemies Of Caragana Korshinskii

The mechanism of three-trophic level between plants,pests and natural enemies is one of the increasing attentions in the field of insect ecology.Meanwhile,one of the worth arguing topic is that the bottom-up and top-down effects between various trophic levels in different ecosystems.Pests and enemies' interaction are affected by landscape pattern changing and landscape fragmentation,Caragana sp.is one of the most important wind-resistant and sand-fixing plant in the desertification area of northwest China.There three main pests of Caragana seed are Etiella zinckenella,Kytorrhinus immixtus and Bruchophagus neocaraganae.The Brachcon nigrorufum is main natural enemy parasitic of seed pests.In this paper,Ningxia Lingwu Baijitan National Nature Reserve was selected as the research area,and 19 caragana patches with typical fragmentation characteristics were selected.In 2019,the pre-mature Caragana pods were picked for stripping and artificial inspection.The feeding experiment investigated the number and damage rate of Caragana microphyll a seed pest in each patch,and the diversity of parasitic natural enemies of seed pests.The impact of the pest-natural enemy's trophic level was analyzed on the population viability of Caragana seed pest-parasitic natural enemies.The main research results and conclusions are as follows:(1)The average number of Caragana sp.grains patches is 3.086 per pod in 19;among the three kinds of seed pests,Etiella zinckenella has the largest number and the most harmful rate,followed by Kytorrhinus immixtus and Bruchophagus neocaraganae.The average number of pests is 0.421 per pod,of which Etiella zinckenella is 0.322 per pod,Kytorrhinus immixtus is 0.081 per pod and Bruchophagus neocaraganae is 0.018 per pod,the average damage rate of Etiella zinckenella is 23.006%,Kytorrhinus immixtus is 2.610%and Bruchophagus neocaraganae is 0.827%;Multivariate correlation analysis of patches perimeter,patches area,and patches inner edge ratio with each trophic level of biomass showed that non-biological factors such as soil physical and chemical factors and water content of patches significantly affected the first trophic level((Caragana korshinskii)biomass,patches connectivity index,plant diversity index,caragana cover percent,natural enemy biomass and other biological factors affect the second trophic level(seed pests)biomass,patches inner margin ratio,plants diversity index and pest biomass are closely related to the third trophic level(parasitic natural enemies).Therefore,the patch pattern has a significant effect on the three trophic levels of Caragana sp.-seed pests-parasitic natural enemies.(2)The 19 patches are divided into 4 plots(BJT A?BJT D)according to their natural location and habitat characteristics,and the hazard rate of seed pests in each plot is BJT D(36.5%)>BJT B(28.9%)>BJT A(27%)>BJT C(22.3%),The Shannon-Wiener diversity index of parasitic natural enemies in each plot showed BJTB(1.688)>BJTD(1.487)>BJTC(1.384)>BJTA(0.687).Multivariate stepwise regression analysis was carried out based on the landscape fragmentation index and the number of seed pests and their damage rate.The results showed that the landscape patch fragmentation index FN,landscape shape fragmentation index FS2 and landscape internal plot area fragmentation index FIt all affected seed pests.The number and hazard rate have a significant impact(R2=0.9992,P=0.0161);Both the patch density index FD and the fragmentation index FI1 within the landscape have significant effects on the diversity of parasitic predators(R2=0.9999,P=0.0256).The multiple stepwise regression of the natural enemy damage control benefit index and the landscape fragmentation index shows that the landscape shape fragmentation index FS2 and the landscape internal plot area fragmentation index FI1 have a significant negative correlation with the natural enemy pollution control benefit index(R2=0.9982,P=0.0420).Therefore,landscape fragmentation has reduced the damage rate of seed pests to a certain extent and increased the diversity of parasitic natural enemies,but it has weakened the natural enemy's control effect.(3)Using the local polynomial regression model and density-area model to study the population survivability of Caragana seed pests and their parasitic natural enemies.The results showed that the minimum suitable habitat of the Etiella zinckenella,Kytorrhinus immixtus and Bruchophagus neocaraganae were 668 m2,700 m2 and 400 m2,the minimum suitable habitat for the dominant species of parasitic natural enemies of Brachcon nigrorufum and Pteromalus orgyiae are 3954 m2 and 800 m2.Respectively,it can be seen that the area required for the survival of parasitic natural enemies is much larger than the suitable habitat of its host.With the nutritional level higher,the minimum suitable habitat is bigger.