Direct and indirect effects of herbivory: Feeding by spittlebugs affects pollinator visitation rates and seedset of Rudbeckia hirta

In this study, I examined the effect of the spittlebug Philaenus spumarius on the reproductive output of the monocarpic forb Rudbeckia hirta. Herbivor es may affect reproductive output either by reducing resources available fo r flower and seed production, or by affecting floral and vegetative plant c haracters, which in turn affect visitation rates bi pollinators. For this p urpose, T examined the effects of four densities of spittlebugs on plant st ature, floral characters, pollination rates, and seed production of R. hirt a. I then used path analysis to compare the relative importance of the reso urce and pollinator limitation pathways. The results indicate that Philaenu s reduces both pollinator visitation rates and the number of flowers per fl ower head, which in turn reduces the number of viable seeds. However, the m ain route v;hereby Philaenus affects seed production ii, by reducing the nu mber of flowers, whereas there seem to be only limited consequences from re ducing pollinator visitation rates. The reduced pollinator visitation rates may still affect total plant fitness by reducing male reproductive success .