The eco-evolutionary drivers belying tropical plant diversity remain a fundamental enigma facing biologists. There is increasing evidence that biotic agents, namely pests and pathogens, may play a key role in the origin of this diversity. Specifically, plants and their specialized enemies are hypothesized to mutually promote diversification via an evolutionary arms race, where plant populations diverge their defenses in response to local enemies, and their enemies adapt accordingly. If this mechanism is indeed occurring, then local adaptation in plant defense should be common in tropical forest. We have previously found evidence for this in tropical tree species spanning the Isthus of Panama – populations from wetter forest were less vulnerable to local herbivory than populations transplanted from drier forest. However, to conclude whether these patterns of vulnerability were actually driven by local adaptation in defense, we must assess directly how our focal plants vary in their defensive chemistry. Leaf material from each population of 10 focal species was collected and foliar secondary compounds were extracted from this material. Though not yet completed, we will use new techniques in untargeted comparative metabolomics to assess whether populations in fact vary in the expression of their defensive chemistry. If so, then specialized herbivores are likely the source, suggesting their role in the generation of tropical diversity.