Investigating the Effect of Longhorned Milkweed Beetle Larval Root Feeding on Resprouting in Common Milkweed

Clonal reproduction is an important form of reproduction for many plants, and plants can grow clonally through a variety of methods, such as belowground stems, specialized organs, or adventitious buds on their roots (Herben and Klimešová 2020). In plants that reproduce via buds on their roots, researchers have shown that damage to roots can stimulate bud production and sprouting (Bartušková and Klimešová 2010). Common milkweed (Asclepias syriaca) is a root- sprouting perennial plant that receives yearly damage to its roots via the feeding of the larvae of the specialist longhorned milkweed beetle (Tetraopes tetrophthalmus) (Erwin et al. 2013). In this study, we tested how the root feeding of the longhorned milkweed beetle’s larvae affects the resprouting, bud production, and growth rate of common milkweed plants. Specifically, we grew common milkweed plants of three different ages (resprouts, juveniles, and seedlings) and then added two densities (moderate and high) of longhorned milkweed beetle larvae to the roots of the plants. Since so few plants resprouted across both study years of 2020 and 2021, we have no evidence that damage influenced resprouting. Moving on to budding, in 2020, the effect of damage on bud production depended on the size of the plants, but, in 2021, we did not see this same interaction. We did however see an effect of damage on growth rate in 2021, where the plants that were not damaged had a higher growth rate than plants that were damaged. In summary, the feeding of the longhorned milkweed beetle’s larvae on common milkweed roots appears to reduce budding, depending on the size of the plant, and reduce the plant’s growth. We conclude that this reduced budding and growth could be important in the field because smaller plants will have reduced flowering, and the plants could also potentially produce fewer sprouts the next year