While many studies have demonstrated the sensitivities of plants and of crop yield to a changing climate, a major challenge for the agricultural research community is to relate these findings to the broader societal concern with food security. This paper reviews the direct effects of climate on both crop growth and yield and on plant pests and pathogens and the interactions that may occur between crops, pests, and pathogens under changed climate. Finally, we consider the contribution that better understanding of the roles of pests and pathogens in crop production systems might make to enhanced food security. Evidence for the measured climate change on crops and their associated pests and pathogens is starting to be documented. Globally atmospheric [CO₂] has increased, and in northern latitudes mean temperature at many locations has increased by about 1.0–1.4 °C with accompanying changes in pest and pathogen incidence and to farming practices. Many pests and pathogens exhibit considerable capacity for generating, recombining, and selecting fit combinations of variants in key pathogenicity, fitness, and aggressiveness traits that there is little doubt that any new opportunities resulting from climate change will be exploited by them. However, the interactions between crops and pests and pathogens are complex and poorly understood in the context of climate change. More mechanistic inclusion of pests and pathogen effects in crop models would lead to more realistic predictions of crop production on a regional scale and thereby assist in the development of more robust regional food security policies.

Abstract.  Recent studies have shown that root‐feeding insects can be of considerable importance in terms of agricultural damage, their indirect impacts on above‐ground herbivores and their efficacy as biocontrol agents of weeds. To date, isolated studies have made it difficult to identify the mechanisms by which soil‐dwelling insects locate and select host‐plant roots. This review synthesizes 78 studies describing root location and selection. Soil insect herbivores do not rely on encountering roots at random, but orientate towards them using semiochemicals that enable specialist insects to distinguish host‐plants from unsuitable plants. Secondary plant metabolites released into the rhizosphere (alcohols, esters and aldehydes representing 37% of reported examples) underpin host‐plant location and recognition, with 80% having ‘attractant’ properties. Insects feeding on a limited range of plants tend to exploit host‐specific secondary metabolites, whereas nonspecialist feeders appear to use more general semiochemicals. When insects reach the roots, contact chemosensory cues act as either ‘phagostimulants’ (48% of the compounds being sugars) or feeding ‘deterrents’ (notably phenolic compounds). Twenty studies conclude that CO ₂ is the major primary plant metabolite that allows insects to locate to roots. However, several features of CO ₂ emissions from roots mitigate against it as a precise location cue. In addition to its lack of specificity, gradients of root emitted CO ₂ do not persist for long periods and vertical gradients of CO ₂ in the soil tend to be stronger than horizontal gradients. A conceptual model is presented, emphasizing the importance of soil properties (e.g. porosity, moisture) on chemical diffusion and insect motility.