Nutrient-specific foraging and the role of spiders as biocontrol agents.

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Spiders are major predators of aphids (and other pests) in cereal crops and are an essential element of pest control in low-input and organic agriculture. However, their economic value to farmers is affected by their density and relative predation rates on pest and non-pest insects. It has been demonstrated in the lab that predators can exercise nutrient-specific foraging to balance their diets (Mayntz et al., Science 2005). Thus, if they have been eating sugar-rich aphids they may preferentially increase predation on protein-rich Collembola or flies.Spiders cannot survive on aphids alone and agriculturalists require guidance on the need to preserve non-aphid prey within crops. However, nutrient-specific foraging has never been demonstrated in the field. Our aim will be to compare what is available to the spiders with what the spiders have eaten. Major nutrients will be analysed for common prey (e.g. Hawley et al., PlosOne 2014). We will analyse diets of spiders using molecular methods then compare what is available with what is eaten, looking for deviations from random feeding that balance their nutrient intake.Mesocosm experiments, informed by prey densities in the field and spider diets, will confirm whether nutrientspecific foraging, rather than other factors, is regulating prey choices.First rotational project - Morphological and molecular identification. This PhD requires expertise in the taxonomy and molecular identification of the species involved. Identification of spiders and 'difficult' prey groups will require training. Relevant species will need DNA barcoding. Training in these areas will primarily be in the lab of WOCS, assisted by JRB at Rothamsted (spiders) and taxonomists in the National Museum of Wales.Second rotational project - Analysis of prey nutrients. A major element within the PhD will be analysis of the effects of major nutrients on prey choice. The student will learn how to conduct the biochemical analyses needed, supervised by CTM. S/he will analyse relevant species from arable fields, establishing their nutrient content and the effects of crop and season.