Interesting. When I first read the summary, I thought it was talking about herbicides and pesticides, only to discover it's talking about plants that are naturally toxic!
Interesting that the specialist caterpillars showed little sign of the toxic elements in their frass, whereas generalist caterpillars did. Aren't Monarch butterflies supposed to 'taste bad' because of all the milkweed consumption as cats? Of course, I guess it could still 'taste bad' even while having the ability to 'sequester' the toxic chemical. Score one for co-evolution!