Document: JEN-3-48-39

Mechanisms underlying increased seed production of Gossypium thurberi (Malvaceae) in the presence of ants.

RUDGERS, J.A.*

University of California-Davis, Davis, CA 95616 USA ¹

Abstract:
Plants may defend themselves against insect damage indirectly by attracting the enemies of their herbivores. A reduction in damage may be realized directly as a result of predation on herbivores, or indirectly via alterations in herbivore behavior in response to the risk of predation. Despite a number of studies documenting benefits to plants in the presence of herbivores' enemies, relatively few investigations have explored the mechanism underlying these benefits. As part of a larger study investigating the evolution of extrafloral nectaries in Gossypium thurberi (wild cotton), behavioral experiments were conducted to determine the mechanism of interaction between ants and the dominant folivore, Bucculatrix thurberiella (Lepidoptera), the cotton leaf perforator. Previous experiments have demonstrated that the presence of ants significantly reduces bud damage by boll weevils, decreases leaf damage by Bucculatrix thurberiella, and increases seed production in wild cotton. However, treatments to exclude ants do not significantly affect caterpillar numbers. Caterpillar behavior was observed simultaneously on ant-accessible and ant-excluded branches of individual plants. On ant-accessible branches, caterpillars were significantly less likely to initiate feeding, were significantly more likely to drop off the leaves and hang by a strand of silk and to drop off the plants. Only four instances of predation were observed during the 1280 minutes of observation. Thus, wild cotton benefits more from ants' interference with, rather than predation on, its primary folivore.

Keywords: ant-plant, mutualism, behavior, Gossypium thurberi, Bucculatrix thurberiella

This abstract is being presented at: 3:30 PM in session:
PLANT-ANIMAL INTERACTIONS