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Title: Crops, Insect Pests and Natural Enemies : Effects of Organic and Conventional Fertilisers
Author: Garratt, Michael P. D.
ISNI:       0000 0004 2675 9939
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2009
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Agricultural intensification can have negative impacts on the environment and there isincreasing interest in the use of low intensity or organic agricultural methods toimprove sustainability. Fertiliser is an important component of all agriculturalsystems and can affect the performance of crop pests and their natural enemies. Thisthesis presents the results from a quantitative review of the literature on both farmingsystem and organic and conventional fertiliser effects on pests and natural enemies. Results from a series of laboratory and field experiments investigating the effectsorganic and conventional fertiliser on cereal aphids and their natural enemies arereported. The review demonstrates that crop pests and their natural enemies benefit fromorganic or low intensity methods and this is evident for natural enemies in farm scaleexperiments. The effect of organic and conventional fertilisers on arthropod pests isvariable although the influence of manures is consistently negative while the effect ofplant composts is positive. More studies investigating organic and conventionalfertilisers and the response of natural enemies are needed. Field and laboratory experiments show that conventional fertilisers can benefit cerealaphids but the mechanism behind this response is species specific. Rhopalosiphumpadi is sensitive to temporal nutrients availability and is influenced by the timing offertiliser application, while Metopolophium dirhodum is responsive to plantmorphology with aphids performing better on plants with a high proportion ofvegetative matter. The implications of pest performance on fertiliser managementstrategies are discussed. Parasitoid abundance in the field was not found to beinfluenced by fertiliser treatment although in the laboratory, indirect effects offertiliser, mediated through its aphid host, were found to affect parasitoid fitness withlarger parasitoids emerging from larger aphids. A positive influence of conventionalfertiliser on syrphid oviposition in the field was also apparent.
Supervisor: Leather, Simon ; Wright, Denis Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral