Host Plant Species Influences the Composition of Milkweed

What this paper is about

Milkweed species differ widely in how much cardiac glycoside they make. This study asked whether that changes the bacteria living on the plant and in the monarchs eating it.

The host plant species shaped both microbiomes, which raises the possibility that some of those bacteria are handling the plant's toxins.

Summarised here from the abstract below. Not the authors’ words.

Abstract

Plants produce defensive chemicals for protection against insect herbivores that may also alter plant and insect associated microbial communities. However, it is unclear how expression of plant defenses impacts the assembly of insect and plant microbiomes, for example by enhancing communities for microbes that can metabolize defensive chemicals. Monarch butterflies (Danaus plexippus) feed on milkweed species (Asclepias spp.) that vary in production of toxic cardiac glycosides, which could alter associated microbiomes. We therefore sought to understand how different milkweed species, with varying defensive chemical profiles, influence the diversity and composition of monarch and milkweed (root and leaf) bacterial communities. Using a metabarcoding approach, we compared rhizosphere, phyllosphere and monarch microbiomes across two milkweed species (Asclepias curassavica, Asclepias syriaca) and investigated top-down effects of monarch feeding on milkweed microbiomes. Overall, monarch feeding had little effect on host plant microbial communities, but each milkweed species harbored distinct rhizosphere and phyllosphere microbiomes, as did the monarchs feeding on them. There was no difference in diversity between plants species for any of the microbial communities. Taxonomic composition significantly varied between plant species for rhizospheres, phyllospheres, and monarch microbiomes and no dispersion were detected between samples. Interestingly, phyllosphere and monarch microbiomes shared a high proportion of bacterial taxa with the rhizosphere (88.78 and 95.63%, respectively), while phyllosphere and monarch microbiomes had fewer taxa in common. Overall, our results suggest milkweed species select for unique sets of microbial taxa, but to what extent differences in expression of defensive chemicals directly influences microbiome assembly remains to be tested. Host plant species also appears to drive differences in monarch caterpillar microbiomes. Further work is needed to understand how monarchs acquire microbes, for example through horizontal transfer during feeding on leaves or encountering soil when moving on or between host plants.

Abstract reproduced from the published paper, which is licensed CC BY. Copyright remains with the authors.

Key terms

RhizospherephyllosphereMicrobiomeMilkweedMonarch

Milkweeds in this paper

Common Milkweed Asclepias syriaca
Tropical Milkweed Asclepias curassavica

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APA

Milkweed USA. (2026). Host Plant Species Influences the Composition of Milkweed and Monarch Microbiomes (listing). Retrieved DATE, from https://milkweedusa.com/research/host-plant-species-influences-the-composition-of-milkweed-and-2022/

MLA

"Host Plant Species Influences the Composition of Milkweed and Monarch Microbiomes (listing)." Milkweed USA, 2026, https://milkweedusa.com/research/host-plant-species-influences-the-composition-of-milkweed-and-2022/. Accessed DATE.

Chicago

Milkweed USA. "Host Plant Species Influences the Composition of Milkweed and Monarch Microbiomes (listing)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/research/host-plant-species-influences-the-composition-of-milkweed-and-2022/.

BibTeX

@misc{milkweedusa_researchhostplantspeciesinfl,
  title  = {Host Plant Species Influences the Composition of Milkweed and Monarch Microbiomes (listing)},
  author = {{Milkweed USA}},
  year   = {2026},
  url    = {https://milkweedusa.com/research/host-plant-species-influences-the-composition-of-milkweed-and-2022/},
  note   = {Accessed DATE}
}

Host Plant Species Influences the Composition of Milkweed and Monarch Microbiomes