ORCID

https://orcid.org/0000-0002-8601-9196

Year

2020

Season

Spring

Paper Type

Master's Thesis

College

College of Arts and Sciences

Degree Name

Master of Science in Biology (MS)

Department

Biology

NACO controlled Corporate Body

University of North Florida. Department of Biology

First Advisor

Dr. Anthony M. Rossi

Second Advisor

Dr. Mike Aspinwall

Third Advisor

Dr. Adam Rosenblatt

Department Chair

Dr. Cliff Ross

College Dean

Dr. George Rainbolt

Abstract

Asphondylia borrichiae is a gall-inducing insect that attacks its ancestral host plant Borrichia frutescens: through ovipositional mistakes it has acquired two additional hosts, Iva frutescens and Iva imbricata. Oviposition results in the formation of a gall, a tumor-like growth of plant tissue within which immature A. borrichiae develop. During development, immature A. borrichiae, are attacked by a suite of four generalist hymenopteran parasitoids. Of these, Galeopsomyia haemon and Torymus umbilicatus are facultative hyperparasitoids, more common and exhibit non-random attack patterns. In the present study, soil quality was manipulated through bi-weekly application of either ammonium nitrate fertilizer or sodium chloride rock salt: resulting in variation in host plant quality. Bottom-up manipulation cascaded upwards through trophic levels and indirectly shifted the composition of the parasitoid guild community. Decreases in host plant quality significantly decreased available leaves (64%), reduced stem growth (17%) and limited growth of the plant and galls when compared to vigorous, higher quality plants. Galls produced from salt-treated plots had significantly lower gall diameter (20%), fewer gall chambers (30%) and significantly increased attacks by G. haemon when compared to control galls (56%). Increasing plant quality significantly increased total leaf size (21%), retained more leaves, and increased growth of the host plant when contrasted with poorer quality plants. Fertilized plants produced galls with significantly greater gall diameter with increased number of T. umbilicatus when compared to controls (12%). Results support the gall-diameter hypothesis as present parasitoids were distributed across gall diameter. This study was successful in changing the natural enemies present within a system through indirect effects of soil quality, these bottom-up effects could potentially shape future top-down control by the parasitoids. Specifically, in instances of potential host-range expansion in which parasitoid composition as mediated by lower trophic levels can either increase or decrease the availability of enemy free space.

Available for download on Wednesday, April 28, 2021

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