eLife Assessment
This important study shows that different forms and mixtures of cardenolide toxins in tropical milkweed, especially nitrogen- and sulfur-containing types, change how monarch caterpillars eat, grow, and store these chemicals under laboratory conditions. It provides solid evidence to demonstrate that chemical diversity within a single group of plant toxins (cardenolides) can have combined effects on even highly specialized herbivores that are different from what one would expect from each toxin alone. However, as all experiments used leaf-disc assays with fixed "natural" toxin ratios and only one adapted herbivore species, tests on living plants, other mixture designs, and non-adapted herbivores would make the broader conclusions stronger.