Document: JEN-3-43-2

Jasmonate-mediated indirect plant defense against herbivores.

THALER, J.S.*

University of Toronto, Toronto, ON CANADA ¹

Abstract:
Plant defenses can act directly by having a negative impact on herbivore preference or performance, or indirectly by enhancing the action of natural enemies. I have been investigating the role of jasmonic acid mediated plant responses in direct and indirect defense of tomato plants in the field. Jasmonate-mediated induction of proteinase inhibitors and oxidative enzymes is associated with decreased preference and performance of several herbivores, and induction of volatiles is associated with increased abundance of parasitoids and mortality of lepidopteran larvae. In the current study, I show that jasmonate mediated responses have a negative impact on aphid populations, but this is not due to effects on natural enemies. Fewer syrphid fly eggs were found on induced plants compared to controls and aphid parasitism was unaffected by treatments. In a large-scale field cage experiment to test the slow growth-high mortality hypothesis for effects of parasitoids on caterpillars, I found that induced plants supported fewer caterpillars (that grew more slowly than controls), but parasitism was unaffected by the slowed larval growth. When I standardized larval density, the effects of the parasitoids were the same: parasitoids killed herbivores, but did not kill more herbivores on induced plants. Thus, for this cage experiment, slow growth of larvae on induced plants did not result in higher mortality.

Keywords: plant-insect interactions, indirect defense, predation, top-down, parasitoid

This abstract is being presented at: 2:30 PM in session:
Oral Session #48: Anti-Predator Responses: Fish to Sagebrush.