Florivores Limit Cost of Mutualism in the Yucca–yucca Moth Association

Multispecies interactions may have important consequences for the ecology and evolution of mutualism by changing the cost-to-benefit ratio. Here I determine whether florivorous beetles can limit moth populations and influence the costs 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 field 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, which translates into an increase in seed production of ;16– 32% per fruit. Counterintuitively, these results suggest that florivores can limit moth populations and reduce the costs incurred by the plant.