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Thiamethoxam and clothianidin are two neonicotinoids used in seed coatings for crops such as corn and soybeans. Both neonicotinoids have high solubility in water, so they are prone to transport via leaching and runoff. This thesis is comprised of two studies that evaluated potential solutions to mitigate neonicotinoid transport from fields. The first study examined the relationship between soil organic carbon content and neonicotinoid transport in a field planted in soybeans. Soils with increased organic carbon leached less thiamethoxam and clothianidin during early growing season leaching peaks; however, at the end of the season, higher organic carbon content only decreased leached mass of clothianidin. The second study was to determine neonicotinoid uptake of different ground covers used as cover crops or edge-of-field buffer strips, as well as the partitioning of thiamethoxam and clothianidin throughout the plants. Ground covers, such as crimson clover, had the highest recovery of applied thiamethoxam, meaning that it may be a good candidate to retain this pesticide in fields. Thiamethoxam and clothianidin concentrations were higher in leaf tissues than in stems or roots, indicating that above-ground biomass removal may be an effective way to reduce neonicotinoid loading in the environment. From these studies, I concluded 1) practices that raise the amount of organic carbon in the soil may help decrease early-season neonicotinoid transport, resulting in lower concentrations in surrounding waterways, and 2) careful selection of plant species, such as crimson clover, may help reduce neonicotinoid transport in the environment, while potentially reducing exposure to beneficial insects.

Ring-necked pheasants (Phasianus colchicus) are economically important to the state of South Dakota bringing in over one hundred million dollars in revenue each season. The population is known to fluctuate temporally for many reasons, often weather related. Unfortunately, no research has been conducted involving ring-necked pheasants that evaluated the impact or interaction of neonicotinoids on the species. The objective of our study was to gain an understanding of how the neonicotinoid, Clothianidin, affects survival and breeding in pheasants. Our first experiment was to determine if there was a selection bias for seeds treated with neonicotinoids. In this experiment, eight ring-necked pheasants (4 hens and 4 roosters) where placed in an enclosure for 10 days. They were provided a choice of three options; untreated, dyed, and dyed/treated seed corn. Seeds were treated with Poncho® 1250 (containing Clothianidin) and dyed with Rhodamine B to match the color of treated seeds. Pheasants selected (P < 0.0001) untreated seeds over dyed and treated seeds. We then collected 185 wild ring-necked pheasant hens from their primary range in South Dakota during the 2017 spring agricultural planting season. We necropsied collected pheasants and collected liver, spleen, and crops. We examined crop contents; 151 (~81.6%) of 185 hens had consumed agricultural seeds and of those 24 (~12.9%) of 185 hens had seeds that had treatment dye. We found that ~15.68% of the hens had greater than 0.5 parts per billion (ppb) neonicotinoid concentrations in livers. Pheasants that had consumed neonicotinoid treated seeds averaged ~3.49 ng/mL Clothianidin versus ~1.90 ng/mL for birds that did not have confirmed treated seeds, which was significantly different (P < 0.04). To test survival of pheasants exposed to Clothianidin in the 2016 field season, groups of 15 captive hen pheasants received seeds of Armor® (Jonesboro, Arkansas, USA) Seed Corn 1046 or Armor® (Jonesboro, Arkansas, USA) Seed Corn 1046 that had been treated with Poncho 1250 (1.25 mg/seed). The five treatment levels consisted of 75 treated seeds, 15 treated seeds, 2 treated seeds, 1 treated seed, and 0 treated seeds (control), which were used in all trials (2016-2017). For the four groups that did not receive 75 treated seeds, untreated seeds were used to fill out the 75 total seeds provided to pheasants. Hens were then monitored for sixty days. After death or euthanasia, hen pheasants were necropsied for lesions or tumors. In 2017, our breeding study consisted of 14 days of treatments for captive pheasants, which were identical to the previous year’s treatments except roosters were included with hen pheasants. There were 5 replicates of 10 hens and 5 roosters. All pheasants received 75 seeds of Armor® (Jonesboro, Arkansas, USA) Seed Corn 1046. The same seed and variety also were treated with Poncho 1250 for the treated seeds. After the 14 days of treatments, hens were placed in breeding cages. Eggs were collected for the 8 days of breeding and 30 days following breeding and placed in an incubator. The 2016 survival results showed support for the null model (AICc 123.88). The survival results from 2017 indicated that the likelihood of survival for pheasants consuming the 75 treated seeds was 0.49 while the other treatments (combined) had a survival probability of 0.83. Survival of pheasant chicks differed; chicks from the 75 seed treatment had a survival rate of 0.50 (SEM = 0.13), whereas survival for 15, 2, 1, and control treatments were 0.73 (SEM = 0.14), 0.81 (SEM = 0.09), 0.62 (SEM = 0.08), and 0.71 (SEM = 0.07), respectively. Our study indicated that pheasants avoid treated seeds, survival probability was lower for pheasants consuming the 75 treated seeds treatment in 2017, and pheasant chick survival and nest initiation were lower and later for the higher treatment levels of Clothianidin.

Neonicotinoid insecticides are currently the most widely used class of insecticides worldwide, accounting for 25% of total insecticide use. They are registered in 120 countries for use on more than 140 crops. Concern has grown, however, over their widespread detection in global surface waters, soil, finished drinking water, and wastewater, and for their potential role in colony collapse disorder in honey bees. This work set out to examine hydrolysis and photolysis reaction rates of neonicotinoids, as well as to identify reaction products and determine the toxicity of the reaction products on mosquitoes. Hydrolysis rates were tested between pH 4 and pH 10. Reaction rates were pseudo-first order and highly pH dependent. Calculated half-lives ranged from >1000 days to 10 days. Divalent metal ions (Cu2+, Ni2+, Zn2+) and minerals (kaolinite, goethite, TiO2) were found to have little to no effect on neonicotinoid hydrolysis. Experiments from pH 4 to pH 10 revealed a non-elementary rate law for neonicotinoid degradation, with the hydroxide concentration being raised to a power of 0.55 ± 0.09. Nitenpyram, imidacloprid, thiamethoxam, and clothianidin were found to undergo direct photolysis, with quantum yields of 0.025 ± 0.001, 0.0119 ± 0.0001, 0.0167 ± 0.0002, and 0.0133 ± 0.0001, respectively. Acetamiprid degraded very slowly via direct photolysis, but was found to undergo indirect photolysis due to reaction with OH∙ with a bimolecular rate constant of 1.7 ± 0.2×109 M-1 s-1. Reaction products were identified for all reactions, with the urea derivative as the most commonly detected product. Toxicity experiments on mosquitoes indicate no residual toxicity from hydrolysis or photolysis products, which may be expected given the removal of the pharmacophore during reactions. While abiotic reaction products were found to be non-toxic, results from experimental work indicates long environmental half-lives for the tested neonicotinoids, which may help to explain their observed persistence in environmental matrices.

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.

The 20 year research focus on residue levels below 10 ppb of neonicotinyl insecticides found in nectar and pollen of seed-treated crops (corn, canola, and sunflower) has not demonstrated a reduction in bee colony health in most field studies. However, the label rate of neonicotinyl use on crops and landscape plants is much higher than seed treatments. In addition, crops and flowers can be retreated multiple times a season which can contribute to chronic exposure to bees at higher residue levels. In an 11 week greenhouse cage study with queenright colonies of Bombus impatiens Cresson, provided 0, 10, 20, 50 and 100 ppb imidacloprid or clothianidin in sugar syrup, neither neonicotinyl reduced production of brood, workers, and queens. Male production decreased in 10-100 ppb imidacloprid and 50-100 ppb clothianidin treatments. However, starting at 6 weeks queen mortality was significantly higher in 20-100 ppb imidacloprid or clothinaidin. The largest impact was the reduction in worker movement, consumption, number of syrup filled wax pots, and the addition of wax to the colony, which resulted in reduced colony weight. Queens and nest bees fed on the sugar syrup stored in wax pots that were filled prior to the start of the experiment. Foraging bees did not return sugar syrup to the nest, but remained on the floor of the flight box. We argue that queen mortality at 20, 50, and 100 ppb was related to lack of syrup in storage pots. We speculate that as queens started to die at week 6, workers in 20-100 ppb treatments produced fewer males and instead provisioned cells to produce new queens, since queen production was not reduced at higher doses, but male production was reduced. Since neonicotinyls in this and other studies were shown to reduce food consumption and foraging, wild bumblebee colonies that depend on workers to forage will be negatively affected by exposure to imidacloprid above 20 ppb. Solitary bees will be greatly impacted as the foraging queens solely provision the larvae.