Multi-species interactions may have important consequences for the ecology and evolution of mutualism, yet relatively few studies have examined whether these interactions influence the population dynamics of mutualists. Here I determine whether florivorous beetles can influence the dynamics of the mutualism between yuccas and their pollinating moths. Yucca moths actively pollinate yucca flowers and their larvae feed on a portion of the seeds. I used a manipulative experiment to examine the hypothesis that the characteristic feeding behavior of the florivorous beetle Hymenorus densus may increase mortality of pollinator moth eggs and reduce the costs incurred by the plant. The results indicated that H. densus consumes moth eggs, and that the consumption rate matches levels of moth mortality typically observed in these populations. On average, beetles consumed 1-2 eggs per flower, reducing the costs incurred to the plant by 16-32 % per fruit. At higher beetle densities, the rate of egg consumption was dependent on the density of moth eggs within flowers. These results suggest that florivores can limit moth populations and may, under certain circumstances, regulate the mutualism between yuccas and yucca moths.
