Journal of Chemical Ecology

, Volume 41, Issue 6, pp 520–523 | Cite as

Secondary Defense Chemicals in Milkweed Reduce Parasite Infection in Monarch Butterflies, Danaus plexippus

  • Camden D. GowlerEmail author
  • Kristoffer E. Leon
  • Mark D. Hunter
  • Jacobus C. de Roode
Rapid Communication


In tri-trophic systems, herbivores may benefit from their host plants in fighting parasitic infections. Plants can provide parasite resistance in two contrasting ways: either directly, by interfering with the parasite, or indirectly, by increasing herbivore immunity or health. In monarch butterflies, the larval diet of milkweed strongly influences the fitness of a common protozoan parasite. Toxic secondary plant chemicals known as cardenolides correlate strongly with parasite resistance of the host, with greater cardenolide concentrations in the larval diet leading to lower parasite growth. However, milkweed cardenolides may covary with other indices of plant quality including nutrients, and a direct experimental link between cardenolides and parasite performance has not been established. To determine if the anti-parasitic activity of milkweeds is indeed due to secondary chemicals, as opposed to nutrition, we supplemented the diet of infected and uninfected monarch larvae with milkweed latex, which contains cardenolides but no nutrients. Across three experiments, increased dietary cardenolide concentrations reduced parasite growth in infected monarchs, which consequently had longer lifespans. However, uninfected monarchs showed no differences in lifespan across treatments, confirming that cardenolide-containing latex does not increase general health. Our results suggest that cardenolides are a driving force behind plant-derived resistance in this system.


Resistance Insect immunity Herbivory Asclepias Danaus plexippus Ophryocystis elektroscirrha 



We thank Jessica Nguyen for help with the experiments and Hillary Streit for help with the chemical analysis. This work was supported by National Science Foundation grants DEB-1257160 and DEB-1256115 to J.C.d.R and M.D.H. K.E.L. was funded by the Summer Undergraduate Research at Emory (SURE) program.


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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  • Camden D. Gowler
    • 1
    • 2
    Email author
  • Kristoffer E. Leon
    • 1
  • Mark D. Hunter
    • 2
  • Jacobus C. de Roode
    • 1
  1. 1.Biology DepartmentEmory UniversityAtlantaUSA
  2. 2.Department of Ecology and Evolutionary BiologyUniversity of Michigan, Kraus Natural Sciences BuildingAnn ArborUSA

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