Plants display extensive intraspecific variation in secondary metabolites. However, the selective forces shaping this diversity remain often unknown, especially below ground. Using Taraxacum officinale and its major native insect root herbivore Melolontha melolontha, we tested whether below ground herbivores drive intraspecific variation in root secondary metabolites. We found that high M. melolontha infestation levels over the last decades are associated with high concentrations of major root latex secondary metabolites across 21 central European T. officinale...