Term of Award

Spring 2002

Degree Name

Master of Science

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Department

Department of Biology

Committee Chair

Daniel V. Hagan

Committee Member 1

C. Ray Chandler

Committee Member 2

Frank E. French

Committee Member 3

Lissa M. Leege

Abstract

Behavioral assays of the parasitic wasp Microplitis croceipes Cresson (Hyrnenoptera: Braconidae) were made at the Coastal Plain Experiment Station, Tifton, GA during the summer of 2001, in a screened in mesh with a 5 X 5 cotton patch. I quantified the influence of plant and host-associated cues and learning foraging behavior, using the interaction between the parasitoid M. croceipes, cotton Gossypium hirsuium L. (Malvales: Malvaceae), and host larvae Helicoverpa zea(Boddie) (Lepidoptera: Noctuidae) as a tritrophic model. Twenty-five cotton plants were arranged in a 5 m x 5 m array, five of which served as treatments that contained different combinations of wasp foraging cues (plant damage, host frass, and host larvae). These manipulated plants are referred to as target plants. Eight different combinations of cues were applied to the target plants: whole damage (all three foraging cues), control (no cues added), plant damage and larva, plant damage and frass, plant damage only, larva and frass, larva only, and frass only. Sequence and duration of hovering, searching, scanning, preening, landing, and stinging were recorded. Behavioral diagrams were constructed to examine the sequence of foraging behavior of M. croceipes in relation to specific combinations of plant and host-associated cues.

Parasitic wasps used a specific behavioral sequence to forage for hosts depending on the combination of foraging cues present. More total time was allocated to target plants in the treatment containing plant damage, larvae, and frass cues combined. Less time was allocated to target plants in the treatment with no cues added.

The comparisons of the number of host stings (which indicates possible ovipostition), the durations of behaviors in relation to the target plants, retention times in the patch and the number of target site visits suggest that plant damage cues were sufficient in aiding wasps in host plant and host location, but that adding frass helped wasps accomplish this more rapidly. Also, comparisons between the patch retention times, duration of behaviors, and number of target sites visited with and without the presence of larvae suggest that contact with larvae improves the rate at which wasps find and successfully locate sites where foraging cues are present, and increase their motivation for searching.

The ability of wasps to allocate less time to foraging behaviors after the prior sting of a H. zea larva and after prior visits to target sites was quantified to show the increase in foraging efficacy by wasp learning. M. croceipes exhibited learning behavior by reducing time spent in all foraging behaviors after host sting and after subsequent landings on target sites for most treatment combinations. The wasps allocated less time to all behaviors combined after subsequent host sting for all treatments that contained larvae and at least one other foraging cue (whole plant damage, damaged plant and larva, and larva and frass). Wasps did not show learning in relation to these behaviors in the larvae only treatment. Parasitoids spent less time searching and hovering after prior sting in the whole plant damage, damaged plant and larva, and larva and frass treatments. Parasitoids allocated less total time when duration of all behaviors was combined for all treatments.

M. croceipes use an efficient system to forage for larval hosts. All components of the tritrophic system (plant, herbivore, and host pest) are important in pest management. Cues emanating from these trophic levels work together in attracting wasps to plants containing signals of herbivore presence. When one cue is absent, host-foraging efficacy is reduced. Learning enhances parasitoids' ability to respond to plant and herbivore associated cues.

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