A new research paper from the University of Florida, published in PLOS ONE, reveals that aphids, commonly known as garden pests, are causing problems for the iconic monarch butterfly. The study focused on tropical milkweed, a nonnative species widely used in the southern U.S., and found that when infested by oleander aphids, the butterflies laid fewer eggs on the plants, and the caterpillars took longer to mature.

Monarch butterflies heavily rely on milkweed and its relatives to complete their life cycle. The study’s findings suggest that aphids on tropical milkweed compromise this crucial resource for monarchs.

The study’s senior author Adam Dale emphasized the importance of planting milkweed in urban areas to support monarch populations. As aphids and similar pests commonly thrive in urban settings, understanding how their outbreaks affect monarch survival is vital, especially on the South’s most commonly used ornamental milkweed species.

The researchers also explored potential reasons behind the negative impact of aphid-infested plants on monarchs. They discovered that tropical milkweed produces chemical compounds called cardenolides to defend against pests, and these compounds increase significantly when infested by oleander aphids. It is believed that the elevated levels of cardenolides may deter monarchs from laying eggs on these plants and affect their caterpillars’ development.

In conclusion, the study highlights the importance of maintaining aphid-free tropical milkweed to give monarch butterflies a better chance of success. The researchers suggest using insecticidal soap to control oleander aphids effectively. However, they acknowledge the need for further research to identify pest management options that keep aphids at bay without harming monarch butterflies. As conservation efforts through landscaping continue, choosing native milkweed species with lower cardenolide levels could be a better option for supporting monarch populations even when aphid levels are high.

References

• Mach, B. M., Long, W., Daniels, J. C., & Dale, A. G. (2023). Aphid infestations reduce monarch butterfly colonization, herbivory, and growth on ornamental milkweed. PLOS ONE, 18(7), e0288407. https://doi.org/10.1371/journal.pone.0288407
• Murray, S. (2023, July 26). Aphids make tropical milkweed less inviting to monarch butterflies, study finds. UF IFAS Blogs; The University of Florida. https://blogs.ifas.ufl.edu/news/?p=38451