Concepts of trait diversity - the key to effective IPM for resilience in arable systems?

Modern agriculture is perceived to be unsustainable having pursued a high productivity, reductionist approach for many decades. The solution proposed for restoring 'sustainability' is often encapsulated in the term 'diversity' but this is frequently as ill-defined and open to wide interpretation as the word sustainable. Key to determining whether diversity is 'the answer' is defining what diversity means in practice in the field. We attempt to describe the concepts and components of diversity and, crucially, how they might combine and interact in agricultural systems. The key concepts are: (1) complexity, (2) variation, and (3) spatio-temporal interaction, with the latter comprising (a) heterogeneity, (b) spatial connectivity, and (c) temporal connectivity. We suggest that this might lead to new strategies of diversity deployment and an index of resilience, a key ingredient of sustainability. These measures of diversity are explored in the context of crop resistance to pests and pathogens and the potential to maximise the benefits for integrated pest management in arable crops.