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Effects of cardenolides of milkweed plants on immunity of the monarch butterfly


Plants and herbivores have co-existed for millions of years, leading to complex relationships. Recent studies of plant–insect interactions have focused on important implications of plant defenses on insect immunity. Plants express defenses against herbivores through the production of toxic secondary chemicals, which may alter immune responses. The monarch butterfly, Danaus plexippus, has been shown to use toxic secondary chemicals (cardenolides) of milkweed plants (Asclepias spp.) to help reduce parasitism. However, little is known about the interaction of these secondary chemicals on the insect immune response. Therefore, we reared monarch caterpillars on five different milkweed species with varying cardenolide levels and measured their immune response to an immune stimulus. In particular, we measured a humoral immune response, in the form of anti-microbial growth, following exposure to lipopolysaccharide (LPS), a bacterial cell wall component. We show that the immune challenge caused a strong humoral immune response in monarch caterpillars. However, the response did not vary with milkweed species and cardenolide concentrations. Our results suggest that the toxins of milkweeds do not directly impact the humoral immune response.

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We thank Erik Edwards for maintaining plants, Miles Holliman and Krish Khurana for assisting with monarch maintenance and injections, and Benjamin Wertz and Huw Davies for providing UPLC technology and training.


This research was funded by the National Science Foundation grant IOS-1557724 to JCDR and IRACDA Fellowships in Research and Science Teaching (NIH K12 GM 000680).

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KLA and JCDR contributed to the study conception and design. Material preparation, data collection and analysis were performed by KLA, AA, and JC. Original draft preparation was written by KLA. Review and editing was performed by KLA and JCDR. All authors read and approved the final manuscript.

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Correspondence to Kandis L. Adams.

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Adams, K.L., Aljohani, A., Chavez, J. et al. Effects of cardenolides of milkweed plants on immunity of the monarch butterfly. Arthropod-Plant Interactions 15, 249–252 (2021).

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  • Monarch butterfly
  • Milkweeds
  • Cardenolides
  • Immune response
  • Zone of inhibition