High diversity of tropical communities is partly due to chemically mediated interactions between plants and insect herbivores. Using large scale transplant experiments and observational studies conducted at neotropical sites from Southern Mexico to Southern Brazil, we documented relationships between plant chemistry, taxonomic diversity, and network complexity, with a focus on the tropical pepper genus, Piper (Piperaceae). We found that attributes that vary with latitude, particularly precipitation, temperature, and biodiversity had strong effects on chemically mediated plant-herbivore interactions. For example, experimental changes in plant diversity had strong but unpredictable effects on herbivore diversity and responses to experimental droughts or floods. Our results clearly support the idea that simple Tilman-style diversity experiments will not yield similar results in complex tropical communities, and that network complexity requires more contextual data on plant traits, land use history, and natural history of herbivores.