Document: JOS-3-48-25

Induced resistance in Catalpa bignoniodes (Bignoniaceae): The rallying of a biotic defense.

NESS, J.H.*, C.R.CARROLL and H.R.PULLIAM

University of Georgia, Athens, GA 30602 USA ¹

Abstract:
The term "induced resistance" describes a reduction in a herbivore's survival rate or reproductive output that is attributable to a response by the host plant. Induced resistance has been documented in a variety of biological systems, and most examples describe some internal alteration within the attacked plant that subsequently exerts a direct effect upon the attacker. However, a plant's defense may extend well beyond these "one-to-one" interactions to incorporate the recruitment of a herbivore's predators and parasitoids. We manipulated damage levels on Catalpa bignonioides (Bignoniaceae) seedlings in order to evaluate whether the ants that visit the plant's extrafloral nectaries would respond as an inducible defense against a specialist herbivore, Ceratomia catalpae (Lepidoptera: Sphingidae). Ants (Dolichoterine spp.) recruited more strongly to leaves that experienced herbivory and/or were occupied by caterpillars in comparison to undamaged leaves, and the initial level of recruitment was positively correlated with damage levels. Exclusion experiments indicated that ant predation can have a significant effect on caterpillar mortality rates, and thus recruitment to damaged leaves may act as an inducible defense on the behalf of the host plant. The cues that elicit this behavior remain unclear. The ant's response to mechanically damaged leaves was similar to that for undamaged leaves, suggesting that the ant response was linked to herbivory rather than simply damage per se.

Keywords: induced resistance, plant defense, extrafloral nectar, ant-plant, Catalpa bignonioides, Ceratomia

This abstract is being presented at: 9:00 AM in session:
Oral Session #5: Mutualisms.