Will those sticky yellow aphids hurt my milkweed plants?
According to research published by UC Davis faculty and students, no.
In fact, honeydew produced by aphids can actually reduce nitrogen in the soil and boost the growth of the milkweeds. UC Davis Professor Louie Yang and three undergraduates, including EERREC scholar Lizbeth Gonzalez, examined the effects of aphid honeydew on milkweeds by mimicking milkweed-honeydew dynamics over one full season. First, they collected honeydew from milkweeds during the summer and in the fall, watered half of their plants with water that contained dissolved honeydew. The other half of the plants received the same amount of water, but no honeydew. The next year, they analyzed soil nitrogen and grew a new set of plants in the honeydew-treated and untreated soil.
The result: adding honeydew reduced inorganic soil nitrogen by over 48%. What's more, milkweed seedlings grew taller and larger when grown in soil that had been treated with honeydew water relative to the control. Potential competitors (cheatgrass and yellow star thistle) did not exhibit this additional growth. Yang suggested that their research emphasizes the potential importance of interactions between plants, herbivores, and soil in communities and ecosystems.
Lizbeth started this project during the 2022 EERREC REU. She also created a video where she explained the research; her segment begins at the 7:21 minute mark.
Congratulations, Louie and Lizbeth!