Cornell University Ithaca, New York, United States
Abstract: Many herbivores sequester plant toxins, and this occurs along a gradient of specialization including “toxic plant generalists” that also consume non-toxic hosts. We hypothesized that availability of toxins for sequestration may trade off with nutritional quality to shape dietary choices in a Lygaeid bug. In the absence of toxins (cardenolides) from a preferred food (milkweed seeds), bugs increased feeding on nutritionally poor, but cardenolide-rich milkweed plant tissue, corresponding to lower growth but greater sequestration. While bugs feeding on only milkweed plant tissue sequestered lower total concentrations of cardenolides than those feeding on seeds, they sequestered more diverse and less polar compounds. There were also substantial differences in total cardenolide concentration, diversity, and polarity between bugs and their food sources, likely a result of selective modification or excretion of specific cardenolides. Cardenolide production was also induced by bug feeding on plant tissues, which may have downstream effects on future herbivory and sequestration. However, this induction was not uniform over time, with cardenolide concentrations peaking after two weeks of feeding. Accordingly, sequestration is a driver of diet choice in this toxic plant generalist, even at the cost of feeding on nutritionally poor plant tissue; reciprocally, plants defensively respond to such feeding choices. Although the prevalence of toxic plant generalism is currently unknown, it deserves considerable attention as a feeding strategy that may allow herbivores to sequester defensive toxins even in the face of variable host-plant availability.
