Herbivory, Plant Density, and Plant Reproductive Success: The Effect of Battus Philenor on Aristolochia Reticulata

The pipevine swallowtail butterfly, Battus philenor, normally consumes °45% of the annual leaf crop of its primary host plant in east Texas (USA), Aristolochia reticulata. Feeding by larvae significantly increases plant mortality and decreases plant growth rate. No direct effects of larval feeding on reproduction were detected, but a substantial decrease in seed production per plant is inferred from the increased mortality and decreased growth rates. Plants grown experimentally at high density had the same probability of having eggs laid on them as did plants grown at low density. The actual number of leaves eaten per plant was also similar for plants grown at both densities. Larval feeding increased mortality and decreased plant growth rate by similar amounts at both high and low plant density. There was also no evidence that seed production was greater at one plant density than at another. The pipevine swallowtail thus does not appear to regulate the density of local patches of Aristolochia. These experimental results do not rule out the possibility of regulation by a numerical response of the butterfly to increases in host population densities throughout large areas of habitat. These results suggest that the pipevine swallowtail has exerted a potent selective pressure molding the evolution of A. reticulata. Three characteristics of this plant species may be interpreted as adaptive responses to this pressure: tough, nutrient—poor leaves; underground flowering and fruiting; and a high root/shoot ratio.

Duke Scholars

Author Mark D. Rausher Biology