Elevational gradients are powerful tools to study the co-evolution between plants and insect herbivores. Classical theory holds that higher abundance and diversity of herbivores at low elevations leads to stronger selection on plant defences. Inconsistency between studies have called into question the generality of this paradigm. With this thesis I explore potential sources of controversy. First elevational gradients could be contingent on plant life-history traits and developmental stage. Second, plants deploy multiple defensive strategies that are usually not simultaneously considered. And third, abiotic factors could influence elevational gradients in plant-herbivores interactions.