Date of Graduation

12-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Entomology (PhD)

Degree Level

Graduate

Department

Entomology and Plant Pathology

Advisor/Mentor

Joshi, Neelendra K.

Committee Member

Lorenz, Gustav M. III

Second Committee Member

Wiedenmann, Robert N.

Third Committee Member

Adamczyk, John J.

Keywords

Agriculture; Entomology; Honey Bee; Imidacloprid; Neonicotinoid; Pollen

Abstract

Bee pollinators provide essential ecological services to wild plant communities, and addtremendous economic value to agriculture by improving both the quality and quantity of crop yield. Beekeepers are often contracted by growers to provide colonies of honey bees for pollination of high-value produce (fruits, vegetables and nuts). Many of the major commodity crops produced in the central and mid-southern United States are wind-pollinated (rice, corn, grain sorghum, wheat), or are sufficiently self-fertile (soybeans, cotton), and so do not require bee pollination in order to produce yield. Beekeepers still rely on these agricultural landscapes to support honey bee colonies when not actively pollinating farms or orchards because these landscapes remain irrigated and productive while other areas may endure a long seasonal nectar dearth. However, intensely managed agricultural landscapes can also expose bees to a variety of detrimental risks, including reduced plant diversity and nutrition, and increased pesticide exposure. Neonicotinoid insecticides have been blamed for recent widespread losses of honey bee colonies in the U.S. and abroad. The planting of insecticide-coated seeds to protect plant growth from early season insect damage has come under particular scrutiny as a potentially significant factor in honey bee declines. Previous investigations have concluded with inconsistent results, based on varying methods employed, seasons and environments, and the scale of the experiments. This study characterized the landscape where seed treatments were common, in terms of floral resources available to bees, sources of contamination. A radius of 2 miles (3.2 km) around an apiary was surveyed for 2 seasons to determine the land use by crop, and to quantify the proportion planted with treated seeds, and what other products were applied during the cropping season, and which of these compounds were found in bee hives. Our survey found that approximately 81% of the landscape was under cultivation, of which 70% was planted with neonicotinoid treated seeds. However, no neonicotinoids were detected in samples of bee hive products. Because pollen could be sampled directly from foraging bees at discrete intervals, and traced back to plant origin, it was used as a bioindicator to determine when neonicotinoids might be present in crops or wild plants. Bees collected relatively little pollen from crops except for a brief period of hot, dry weather. Neonicotinoids were detected infrequently and at low levels, and not at all when bees were visiting crop plants. To test the effects of neonicotinoid ingestion on individual bees in situ, a method was devised to continuously monitor the activities of individual honey bees fed with a sublethal concentration of imidacloprid. Bees that consumed 20 ppb imidacloprid did not suffer acute mortality, but actually appeared to survive 1.7 times as long as untreated bees. This work suggests that neonicotinoids, when properly utilized, may not necessarily pose a greater risk to honey bees than other agricultural chemicals, provided colonies have access to sufficient alternative nutritional sources in the surrounding landscape.

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