1. Density- and trait-mediated indirect interactions (DMIIs and TMIIs, respectively) are important drivers of community dynamics, but how plant nutrients (bottom-up effects) affect the magnitude of such indirect interactions has been scarcely addressed. 2. To assess the impact of bottom-up forces on indirect interactions, we carried out lab and greenhouse experiments manipulating plant nutrient supplies in a four-species diamond food web consisting of a plant (tomato), two phytophagous insects (a leafminer and an aphid), and a predator (a mirid bug) attacking both herbivores. 3. Multiple negative indirect effects of the leafminer occurred toward the aphids. The presence of its eggs reduced aphid population growth through increased predator abundance (DMIIs), and larval herbivory both slowed down aphid development and negatively affected aphid behavioural pattern (TMIIs) e.g. they spent less time feeding; likely owing to enhanced plant chemical defences and/or its decreased nutritional quality. Moreover, the low plant nutrient supply further magnified TMIIs. 4. Abiotic factors modulated predator- and plant-mediated indirect interactions among herbivorous community members. Our study highlights the importance of a holistic approach, from foliar chemistry to community dynamics, for disentangling interspecific interactions in a simple food web.