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Abstract
Nutrients mediate a sprawl of ecological interactions, challenging our ability to predict basal trophic cascades. Diet breadth determines unique consequences of nutrients for herbivorous insects, with specialists less tied to plant quality than generalists. Predator responses also vary by diet breadth; foliar-feeding omnivores respond to plant quality, while generalist predators may lack direct links to nutrient availability. Here, we manipulate a gradient of soil fertility in a field of two model host plants, zucchini and tomato, and measure responses of herbivores and predators that vary in diet breadth. Diet breadth mediated responses to fertility across trophic levels, with specialist and generalist herbivores exhibiting unique responses to fertility on zucchini. Foliar-feeding omnivores had positive responses fertility on both host plants, while generalist predators had a neutral response. Rather than promoting herbivore outbreaks, our results suggest that bottom-up effects of nutrient availability might come back around as top-down control via omnivore recruitment.