Managing fertility with animal waste to promote arthropod pest suppression

Fertility management is key to maintaining soil quality in crop systems and can have important implications for plant growth and insect pest populations. Organic fertility amendments, particularly animal manures, are hypothesized to simultaneously promote plant vigor, herbivore resistance, and top-down pest suppression. Animal-waste fertilizers influence pest control in at least two ways: first, they can affect prey suppression from the bottom up by changing macro- and micronutrient concentrations in the plant, shaping the rhizosphere community, elevating production of defensive chemicals and altering herbivore-induced plant volatiles (HIPVs). Second, animal-waste fertilizers can affect conservation biological control from the top down by improving the soil-surface habitat for predators through altered soil tilth, organic matter, water retention, and by supporting decomposers communities that also feed soil-dwelling predators as non-pest prey. However, while animal-waste fertilizers may enhance pest suppression when applied correctly, when manure is overused there are also costs of excess fertility pest management and water quality. In this review of the existing body of research on interactions between animal-waste fertilizers, herbivores, and natural enemies, we summarize trends, report costs and benefits, and identify research opportunities for future studies.