Masters Theses

Date of Award

8-2016

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

John A. Skinner

Committee Members

Scott D. Stewart, Andrea L. Ludwig

Abstract

The current decline of the honey bee (Apis mellifera L.) and other beneficial pollinator species is well documented. Several causes have been cited in this decline including: pathogens, pests, nutrition, and pesticide exposure. Since the advent of the neonicotinoid family of pesticides in the 1990’s an increase in honey bee colony loss has been observed. Neonicotinoid pesticides are commonly applied as a seed treatment to cotton, soybean and maize row crops. As the seed germinates, it absorbs the pesticide from the coating then spreads systemically throughout the entire plant. However, a large portion of the seed coating may stay in the soil, possibly having unintended consequences. To determine whether neonicotinoid compounds from treated seed are transported from application sites we examined soils adjacent to soybean fields for neonicotinoid pesticide at several distances from field borders as evidence of transport from seed treatments via soil-water processes Neonicotinoid content was sampled in soils of experimental plots at the University of Tennessee’s East Tennessee Research and Education Center (ETREC), Plant Sciences Unit. Soybeans treated with the neonicotinoid thiamethoxam (Cruiser) were cultivated in the test field and untreated soybeans were planted in a check field which had been previously planted with clothianidin seed treated maize in 2014. Both plots were in a maize/soybean rotation with soybeans in 2015 and maize in 2016. Soil samples were tested for neonicotinoid content using the QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method by the USDA AMS Laboratory in Gastonia, North Carolina. Soil tests indicated no thiamethoxam at the 1 ppb limit of detection (LOD), although concentrations of the thiamethoxam metabolite clothianidin were found. Initial conclusions suggest that the neonicotinoid thiamethoxam was not found in adjacent soils but its metabolite clothianidin was present in measurable concentrations. Clothianidin detected in collected soil samples was not in concentrations known to be harmful to honey bees. The clothianidin found in adjacent soils may be the result of either microbial metabolism of thiamethoxam or residual deposits from clothianidin treated maize from 2014, or both.

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