Date of Award

1-1-2011

Document Type

Campus Access Dissertation

Department

Biological Sciences

First Advisor

David E Lincoln

Second Advisor

David S Wethey

Abstract

Learned attraction to herbivore-related plant volatiles provides a simple but effective mechanism to increase parasitoid foraging effectiveness. Hypotheses that learned attraction is dose dependent, that parasitoid wasps use elemental processing during learning, and that the concentration during learning of herbivore-related plant volatiles affects attraction responses were tested using a novel technology which controlled the concentration of herbivore-related plant volatiles. Two-day old females of Cotesia congregata (Say) (Hymenoptera: Braconidae) were conditioned by oviposition in larvae of Manduca sexta (Lepidoptera: Sphingidae) and their learned attraction was assayed 18-24 hours after conditioning in a Y-maze olfactometer. Wasps were conditioned in the presence of the complete volatile blend emitted by wounded tomato leaves (Solanum lycopersicum `Castlemart') and their attraction was assayed using controlled dose/emissions of cis-3-hexen-1-ol (green leaf volatile), ├â┬ƒ-caryophyllene (induced volatile), 2-carene (constitutive volatile), and a blend of the three components. Wasp attraction was concentration dependent for all three compounds, as well as the blend, with attraction observed over five orders of magnitude, usually in a log-linear response. Wasp attraction to a blend of components did not increase relative to the individual compounds, suggesting predominately elemental processing of olfactory signals. When wasps were conditioned over a range of concentrations of β-caryophyllene, attraction to a single high concentration of β-caryophyllene showed a positive log-linear relationship, with peak attraction at the concentration to which they were conditioned. When wasps were conditioned by oviposition with a single low concentration of β-caryophyllene, learned attraction generally increased relative to unconditioned individuals, and the response curve was hill-shaped with a peak at the concentration at which conditioning occurred. These results indicate that wasps learn the concentration of herbivore-related plant volatiles and have attraction responses that are specific to the learned concentration. Wasps of C. congregata appear to be able to perceive, learn, and are attracted to a wide range of volatile concentrations, including those of constitutive volatiles, in a manner that may allow host searching behavior to use continuous concentration differences, and the concentration a parasitic wasp encounters during learning and host searching seems to be an independent and important factor in understanding parasitoid behavior in tri-trophic interactions.

Share

COinS