Date of Award:

5-1-2007

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Life Sciences: Biology

Committee Chair(s)

William A. Brindley

Committee

William A. Brindley

Committee

Jordi Bosch

Committee

Rosalind R. James

Committee

John Evans

Committee

William P. Kemp

Abstract

Pollination of alfalfa seed crops is done primarily by managed populations of the alfalfa leafcutting bee, Megachile rotundata (F.). One of the biggest problems associated with managing M. rotundata on a commercial scale is a fungal disease called chalkbrood, caused by Ascosphaera aggregata Skou. The disease infects larvae that have consumed pollen and nectar contaminated with fungal spores. The spores germinate in the bee's gut, spreading hyphae throughout the host and killing the bee. Mortality from chalkbrood is regularly 10% to 35% in the northwestern United States, and infection levels in excess of 50% are not uncommon. As a consequence, alfalfa seed growers in the U.S. must supplement their bee populations annually by purchasing bees from areas of Canada with very low chalkbrood levels. The objectives of this thesis were to 1) develop a series of quick, easy, and inexpensive laboratory tests to screen fungicides for possible use in chalkbrood control programs, and 2) begin identifying those fungicides showing potential for chalkbrood control for later field experiments. A prospective fungicide must have a toxic effect on the fungus without harmful effects to larval and adult stages of the bees. This study addressed the efficacy and non-target effects of four fungicides: Benlate®, Captan®, Orbit™, and Rovral®. Fungicides were evaluated in three areas: 1) effectiveness in inhibiting fungal growth in laboratory cultures of A. aggregata, 2) effects on incidence of chalkbrood and mortality in M. rotundata larvae after incorporation of fungicides into the pollen-nectar provisions, and 3) effects on adult M. rotundata mortality from contact and oral exposure to fungicides. Results of this study identified Benlate® and Rovral® as the most promising fungicides for further studies. Both reduced fungal growth and incidence of chalkbrood with minimal negative toxicological effects on larval and adult bees. Orbit™ was effective in reducing fungal growth, but did not reduce incidence of chalkbrood and was toxic to both larval and adult bees. Captan® was not effective in reducing fungal growth and chalkbrood, and was toxic to both larval and adult bees. Contact tests with treated filter paper were not useful in assessing the toxicity to adult bees.

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