The decline of honey bee (Apis mellifera) colony numbers in recent years presents an economic and ecological threat to agriculture. One outstanding threat to honey bees is the unintended exposure to agricultural pesticides. Previous studies report that acute exposures to the common-use herbicide atrazine elicit oxidative stress in non-target insects; however, little information is currently available on the exposure risk of atrazine to honey bees. This project examined biochemical and molecular oxidative stress response markers of honey bees following laboratory and field treatments of atrazine. Laboratory experiments were conducted with honey bees exposed to increasing concentrations of atrazine for 24 h whereas hive experiments were conducted with bees exposed to one sub-lethal concentration of atrazine for 28 d. The overall antioxidant enzyme activities of atrazine-treated honey bees were decreased compared to the untreated honey bees in both the laboratory and hive experiments. After exposure to atrazine in the laboratory and field, semi-quantitative RT-PCR analysis of antioxidant-encoding genes reveals the differential expression of genes in atrazine-treated bees that are important for oxidative stress tolerance in the laboratory and field experiments. Here, we provide evidence that the laboratory and hive exposure of honey bees to the common-use herbicide atrazine results in oxidative stress responses that can compromise the health of bee colonies. The data will be discussed with regard to the protection of these pollinators against the untended exposure of agricultural pesticides. / Master of Science in Life Sciences / The pollination service provided by insects, primarily honey bees, is estimated to contribute approximately one-third of the diet consumed by the average American. Honey bees are vitally important pollinators due to their broad range of foraging activities and ease of husbandry within a managed colony. In recent decades, colony numbers have decreased in the developed areas of the planet and pesticide usage has been implicated in these losses. Atrazine is the second most commonly used agricultural herbicide in the country and has been linked to oxidative stress in beneficial insects in the past. Oxidative stress is the result of an uncontrolled build-up of reactive oxygen species in an aerobic organism. These reactive oxygen species are dangerous because they are capable of damaging proteins, DNA, and cell walls. Every aerobic organism also possesses antioxidant function which serves to prevent or counteract damage caused by reactive oxygen species. This study examined antioxidant enzyme activities and antioxidant-encoding gene expression levels, which were used as indicators of oxidative stress biomarkers, in honey bees exposed to atrazine in the laboratory and in the hive environment. Honey bees were exposed to atrazine at increasing concentrations in the laboratory for 24 h and at one environmentally relevant dose for 28 d in the hive. After exposure to atrazine in the laboratory and the hive, four out of five antioxidant enzyme levels of honey bees decreased which implied an increase in oxidative stress and a decrease in antioxidant defenses. Activity of one enzyme, lipid peroxidase, increased in honey bees after exposure to atrazine. Lipid peroxidase is the most common measure of cellular injury during oxidative stress, once again signifying an increase in reactive oxygen species production and oxidative stress. Expression levels of seven antioxidantencoding genes were examined in honey bees after atrazine exposure and expression levels of some genes changed compared to the untreated control and expression levels in some genes remained the same compared to the untreated control. These changes in antioxidant-encoding gene expression levels may imply an increase in oxidative stress due to exposure of the honey bees to atrazine. This study aimed to examine biomarkers of oxidative stress in honey bees exposed to the commonly used herbicide atrazine with the hope of raising awareness of harmful effects caused by atrazine and protecting these important pollinators from unintended exposure to agricultural pesticides.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/72949 |
| Date | 14 September 2016 |
| Creators | Williams, Jennifer Rae |
| Contributors | Entomology, Anderson, Troy D., Fell, Richard D., Brewster, Carlyle C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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