ABSTRACTPlants produce chemicals (or plant specialised/secondary metabolites, PSM) to protect themselves against various biological antagonists. Herbivorous insects use plants in two ways: as a food source and as a defence source. Insects can detoxify and sequester PSMs in their bodies as a defence mechanism against predators and pathogens. Here, I review the literature on the cost of PSM detoxification and sequestration in insects. I argue that no-cost meals might not exist for insects feeding on toxic plants and suggest that potential costs could be detected in an ecophysiological framework.