Herbivore-herbivore interactions complicate links between soil fertility and pest resistance

Soil fertility is tightly linked with herbivore pressure because it affects the nutritional status of host plants as well production anti-herbivore defenses. This in turn can influence whether herbivores different feeding guilds render more or less susceptible to one another. Thus, growers’ management choices may impact through a variety indirect channels. We examined relationships between soil and interactions phloem-feeding leaf-chewing on broccoli (Brassica oleracea) greenhouse, taking advantage natural variation nitrogen (N) phosphorus (P) soils from 20 working organic vegetable farms. Next, we experimentally fertilized field trial N and/or P examine consequences these nutrients for growth specialist generalist herbivores. Soils our cooperating farms varied widely concentrations, 40% exceeding recommended pre-plant concentrations 90% recommendations. In single-herbivore infestations, augmenting increased caterpillar (Pieris rapae) growth, augmented additively enhanced green peach aphid (Myzus persicae) colonization, (but not N) cabbage (Brevicoryne brassicae) growth. dual-guild caterpillars facilitated absence fertilizer, but this pattern disappeared under N, reversed P. found that complex web effects performance, depending identity being altered, ecological roles responding species (i.e., versus generalist), chewing sucking More generally, highlight successful use improve pest resistance requires careful consideration niches herbivore-herbivore interactions.