Publication Date

5-2013

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Biology

Department

Biology

Major Advisor

Merlin M. White, Ph.D.

Abstract

Pesticides are widespread and have been long used to combat the attack and destruction of crops. Fungicides have been used to prevent the establishment of many fungal pathogens, yet little is known about the impacts of fungicides on non-target fungi. With these considerations, it was predicted that trichomycetes, or gut fungi, a group of symbiotic fungi associated with aquatic macroinvertebrates and other arthropods, might be a candidate system to study because of the intimate association with their hosts. Field and laboratory studies were initiated to assess non-target impacts of fungicides on gut fungi. Field surveys were conducted on four streams with varying pesticide inputs in Southwestern Idaho. Larval black flies (Diptera: Simuliidae), hosts to many gut fungi, were analyzed for a suite of currently used pesticides including fungicides. The infestation rate and density of gut fungi in hosts residing in streams within agricultural watersheds was lower than those residing in reference streams. Fungicides were detected in hosts collected from streams within agricultural watersheds, but not in those from reference streams. These findings suggest that there may be an effect of fungicides on non-target fungi. Laboratory investigations were designed to test this hypothesis using both host-fungus microcosms and in vitro experiments with axenic fungal cultures. Pure strains of host black fly larvae, Simulium vittatum IS-7, and the gut fungus Smittium simulii, were exposed to the fungicide azoxystrobin. With direct in vitro exposure, a significant decrease in dry weight of the gut fungus was not observed until 0.5 mg/l of azoxystrobin, approximately three orders of magnitude higher than what was detected in the field. In two of three microcosms, there was no statistically significant effect of fungicides with maximum concentrations as high as 5000 ng/l. Attempts to test the higher concentrations in the microcosm experiments were preempted by 100% mortality of the black fly larvae. It is likely that azoxystrobin alone was not the cause of decreased percent infestation and density observed in the field. Data generated from this study indicate the need for future studies to better understand the effects of fungicides and other currently-used pesticides on non-target fungi.

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