The Effects Of Landscape Compositions On Aphid-parasitoid Food Web Structure In Cotton Fields Of Northern China

The study further optimized the cotton aphid-parasitoid multiplex PCR system.With this PCR system,we systematically analyzed the variation of cotton aphid-parasitoid food web structures,parasitoid diversity and parasitism rates in different agricultural landscape compositions.The main results are listed below.1.The optimization of cotton aphid-parasitoid PCR systemBased on the previous research,we focused on four hyperparasitoid species,Syrphophagus aphidivorus,Syrphophagus sp.,Syrphophagus taeniatus and Syrphophagus eliavae to accomplish a comprehensive PCR detection technique.According to the COI sequences,two pair of specific primers were designed and two single PCRs(SP7,SP8)targeted on Syrphophagus spp.and S.eliavae were established.The sensitivity of the primers was 10000 and 1000 copies respectively.The optimized PCR detection system can detect more parasitoid species and obtain more comprehensive cotton aphid-parasitic food web information.This shall provide the technical base for the research of cotton aphid-parasitoid food webs.2.The analyses of cotton aphid-parasitoid food web structures in different landscape compositions1)The twenty-five experimental sites were selected in northern China.The investigation of mummy aphid population and the collection of aphid mummy samples were conducted in each site and found One aphid(Aphis gossypii),three primary parasitoids and seven hyperparasitoids species or genus were found in the sample detection with the optimized aphid-parasitoid mutiplex PCR system.The dominant of primary parasitoid species was Binodoxys communis(> 80%)and hyperparasitoids were Syrphophagus spp.(> 35%).2)The landscape composition and parasitism rate of A.gossypii,the diversity of parasitoid and the parameters of quantitative food web were analyzed by multivariate regression analysis and AICc model screening.The correlation among parasitism rate,diversity of parasitoid and quantitative food web parameters was evaluated by linear regression.It was found that the parasitism rate of A.gossypii could be indirectly affected by landscape pattern.The landscape effect was mainly regulated by the diversity of aphid parasitoid and food web structure.The parasitism rate of A.gossypii had weak positive relationship to the proportion of noncrop habitat and negative relationship to the hyperparasitoid diversity,the links per species and generality of primary parasitoid-hyperparasitoid food web.Nevertheless,the diversity and links per species of primary parasitoid-hyperparasitoid food web was negatively related to cotton planting proportion.The species richness of hyperparasitoid was positively related to the planting proportion of maize and non-crop habitat.This indicates that landscape composition can directly affect the parasitoid diversity and food web structure,while the food web structure can directly affect the parasitism rate in the cotton field.The more hyperparasitoid abundance,the more links of primary-hyper parasitoid food web,the more complex food relationship,the higher the generality,the lower the average proportion of connections per species(connectance),which could promote the control of the primary parasitoid by hyperparasitoid,resulting in a decrease of parasitism rate and control.In this study,we further optimized the cotton aphid-parasitoid multiplex PCR which could be used for the detection of more diversified species and obtain more comprehensive aphidparasitoid food web information.Meanwhile,the comprehensive analysis of landscape pattern effect on cotton aphid-parasitoid food web was conducted to provide evidence to utilize the biocontrol efficiency and develop the innovative cotton aphid IPM strategy.