THE CONSEQUENCES OF FLORAL HERBIVORY FOR POLLINATOR SERVICE TO<i>ISOMERIS ARBOREA</i>

Abstract

Flower-feeding insects may reduce the reproductive success of their host plant in subtle ways that go beyond a direct reduction in gametes. Pollinators may respond to floral damage by visiting damaged plants at lower rates. Fewer visitations to the plant may result in fewer flowers that receive pollinator service and as a consequence lead to lower male and/or female reproductive success. In a two-year study, we examined the direct effect of flower predation by Meligethes rufimanus on the floral display of Isomeris arborea, and the indirect effect of herbivory on pollinator behavior. Plants exposed to herbivore attack produced fewer functional inflorescences than plants protected from herbivory. Undamaged flowers produced three times as much nectar per flower as damaged flowers. Likewise, protected plants had over twice as many anthers per flower as exposed plants. Pollinators responded by visiting damaged flowers less, and exposed plants had lower flower visitation rates than protected plants. Pollinators also visited patches of protected plants more frequently than exposed patches. These results show that floral herbivory reduces pollinator service and thus may reduce reproductive success indirectly, as well as through the direct consumption of viable gametes.