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Effects Of Landscape Pattern On Enemy Abundance And Its Control Of Wheat Aphids In Northern China

Posted on:2017-02-27Degree:MasterType:Thesis
Country:ChinaCandidate:L YangFull Text:PDF
GTID:2283330485487224Subject:Agricultural Entomology and Pest Control
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In spring, there are large amounts of predators and parasitoids in wheat fields, which subsequently act as the major source of natural enemies in cotton fields. The enemy abundance in wheat fields usually affects the biological control of cotton insect pests. In order to determine the effect of landscape pattern on enemy occurrence at a large scale, and then to develop the strategy of enemy conservation in wheat-cotton ecosystem, we investigated the population dynamic of wheat aphids and enemies in wheat fields within different agricultural landscapes at three developmental stages, i.e., elongating stage, flowering stage and milk-ripening stage. We also identified the land use pattern by ground verification, then used adjusted Akaike’s information Criterion(AIC c) to compare the general linear models containing principal landscape variables and landscape diversity at four different scales(0.5, 1.0, 1.5, and 2.0 km), and analyzed the effects of landscape pattern on biological control of wheat aphids at each stage. The main results were summarized as follows.1. In northern China, the non-crop habitats such as forest, fallow and village in the agricultural ecosystem were available for the population increase of ladybeetles in wheat fields at all three stages, but not for the landscape diversity. Landscape features at 0.5 km and 1.0 km were best predicted ladybeetle abundance at elongating stage and milk-ripening stages, respectively. While the best fit model of the ladybeetle abundance at flowering stage was at 2.0 km scale. Propylaea japonica as the dominant ladybeetle specie in wheat fields had the same relationship with landscape parameters as the whole ladybeetle population.2. At flowering stage, the species richness and diversity of aphid parasitoids were best predicted by landscape variables at 2.0 km and 0.5 km respectively, and non-crop habitats in agricultural landscape facilitated the species richness and diversity of parasitoids. However, the landscape diversity index had a negative effect on parasitoid diversity. Non-crop habitats enhanced the abundance of mummies at elongating and flowering stages. The rate of parasitism at elongating stage has a positive relation with the wheat area, but non-crop habitats enhanced the parasitism at flowering stage. Hyper-parasitoids were more sensitive to landscape pattern than primary parasitoids.3. The population density of aphids at elongating stage was negatively correlated with the proportion of wheat field at all the scales, and the best fit model was found at 1.5 km. At flowering stage, no significant relationship between aphid abundance and different landscape variables was found. However, at elongating and flowering stages, aphid growth rate was positively corrective with the planting area of wheat in the agricultural landscape.
Keywords/Search Tags:agricultural landscape, ladybeetle, parasitoid, wheat aphid, biological control
PDF Full Text Request
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