Hadley Copeland
University of Georgia
November 2025
Background
Across the Southern Appalachian Mountains, salamanders are an important component of stream ecosystems kept cool and damp by hemlock canopies. Salamanders are among the most abundant vertebrates in these forests, influencing decomposition, nutrient dynamics, and contributing to connections between aquatic and terrestrial food webs. Yet, like so many amphibians worldwide, they now face a suite of emerging threats: habitat degradation, climate change, and exposure to chemicals or other pollutants.
One chemical drawing new attention is imidacloprid, a neonicotinoid insecticide designed to target insect brains (1). Imidacloprid is widely used to combat the invasive hemlock woolly adelgid (Adelges tsugae), which is devastating eastern (Tsuga canadensis) and Carolina hemlock (Tsuga carolinana) stands and rendering the habitat inhospitable to many species (2). This insecticide is systemic, meaning it can stay in organic matter for long periods of time, allowing forest managers to reduce the frequency of applications they need and making it a worthy choice for sensitive applications (3). However, this persistent nature makes it capable of leaching into streams slowly over time, which has recently become a concern due to evidence that stream salamander abundance may be lower in areas where imidacloprid has been used to protect hemlocks (4).
Imidacloprid and its metabolites have been shown in other amphibians to affect the liver, kidneys, and even their brain, highlighting its ability to cross the blood-brain barrier and potentially alter normal functions and behaviors (5-7). For salamanders, these subtle effects could have ecological consequences. Many Appalachian stream species, including Nantahala Black-bellied salamanders (Desmognathus amphileucus) and Blue Ridge Two-lined salamanders (Eurycea wilderae), spend months to years as aquatic larvae, and remain closely associated with streams their entire lives (8). Any change to how they forage, respond to danger, and grow during this critical stage could influence survival and population dynamics later on.
This is especially relevant in the southern Appalachians, where endemic and highly restricted species like the Patch-nosed Salamander (Urspelerpes brucei) share the same habitats and ecological niches as the more common species I study (9). Because U. brucei occurs in only a few nearby streams, D. amphileucus and E. wilderae can serve as important surrogates, helping us understand risks to sensitive salamanders without disturbing their populations directly.
My masters research explores these potential sublethal effects of imidacloprid exposure on stream-breeding salamanders, focusing on physiological and behavioral responses that may indicate neurotoxicity. I am particularly interested in determining toxicological pathways that help us understand the gap between observed salamander declines and the underlying biological mechanisms driving them. By examining the risks imidacloprid poses to salamanders in headwater systems, our findings provide valuable insight for forest managers seeking to balance invasive species control, hemlock conservation, and long-term amphibian population resilience.
Methods
I am combining field surveys with laboratory exposure experiments. Laboratory studies allow for better control of exposure. We will use field studies to confirm the relevance of laboratory studies.
In the field, I am studying twelve streams that vary in hemlock density and management history. At each stream, I survey plots for larval salamanders, turning rocks, leaf litter, and woody debris to locate individuals while recording environmental variables like substrate type, canopy cover, and water flow. During this sampling, I also collect a small number of salamanders for laboratory analyses to look at their feeding behavior, brain structure, and imidacloprid concentrations in their body tissues.
In the lab, I have been conducting a series of experimental exposure trials designed to mimic environmentally realistic imidacloprid levels. Salamanders are housed in chilled, circulating stream channels and treated with control, low (1 ppb), or high (10 ppb) doses of imidacloprid for defined periods. Over time, I record how much time they spend under cover versus exposed, their feeding activity, and their growth and survival. Then I conduct the same physiological and behavioral laboratory analyses as the field survey, along with additional measures to monitor stress responses.
Preliminary Results and Next Steps
This past spring I completed a pretreatment field season before forest managers applied imidacloprid treatments over the summer. I will return next spring for post-treatment sampling, which will help reveal any changes in abundance, size, or condition following treatment. Experimentally, I have completed two one-month exposure rounds using each of our study species, with early results showing that both salamander species maintained no significant change in growth. However, these findings raised new questions about whether longer exposures that are more consistent with their larval period might reveal more.
To date, I am currently halfway through a longer three-month trial with D. amphileucus, which should provide insight on a more chronic pulse exposure. Next spring, I will return to the field for post-treatment surveys, completing the second half of my paired pre- and post-treatment comparison. This will allow me to directly assess how larval salamander populations respond to imidacloprid use in the wild, and connect any patterns I see in natural populations with the physiological mechanisms I am currently revealing in the lab.
With the support of the Orianne Society, I have been able to expand the scope of my analyses, giving us a more complete picture of how imidacloprid interacts with headwater ecosystems. The findings from this work aim to help forest managers balance hemlock conservation and amphibian protection by refining treatment methods that minimize runoff risks while maintaining the ecological integrity of southern Appalachian streams.
Literature Cited
- Crayton, S. M., Wood, P. B., Brown, D. J., Millikin, A. R., McManus, T. J., Simpson, T. J., Ku, K.-M., & Park, Y.-L. (2020). Bioaccumulation of the pesticide imidacloprid in stream organisms and sublethal effects on salamanders. Global Ecology and Conservation, 24, e01292. https://doi.org/10.1016/j.gecco.2020.e01292
- Vose, J. M., Wear, D. N., Mayfield, A. E., & Nelson, C. D. (2013). Hemlock woolly adelgid in the southern Appalachians: Control strategies, ecological impacts, and potential management responses. Forest Ecology and Management, 291, 209–219. https://doi.org/10.1016/j.foreco.2012.11.002
- Van Meter, R. J., Glinski, D. A., Hong, T., Cyterski, M., Henderson, W. M., & Purucker, S. T. (2014). Estimating terrestrial amphibian pesticide body burden through dermal exposure. Environmental Pollution, 193, 262–268.
- Maerz, J. C., & McCarty, E. (In Press). Abundance of Southern Appalachian Plethodontid salamanders in response to imidacloprid exposure.
- Campbell, K. S., Keller, P. G., Heinzel, L. M., Golovko, S. A., Seeger, D. R., Golovko, M. Y., & Kerby, J. L. (2022). Detection of imidacloprid and metabolites in Northern Leopard Frog (Rana pipiens) brains. Science of the Total Environment, 813, 152424. https://doi.org/10.1016/j.scitotenv.2021.152424
6 . Ade, C. M., Boone, M. D., & Puglis, H. J. (2010). Effects of an insecticide and potential predators on green frogs and northern cricket frogs. Journal of Herpetology, 44(4), 591–601.
- Lee-Jenkins, S. S. Y., & Robinson, S. A. (2018). Effects of neonicotinoids on putative escape behavior of juvenile wood frogs (Lithobates sylvaticus) chronically exposed as tadpoles. Environmental Toxicology and Chemistry, 37(12), 3115–3123. https://doi.org/10.1002/etc.4284
- Hocking, D. J., Crawford, J. A., Peterman, W. E., & Milanovich, J. R. (2020). Abundance of montane salamanders over an elevational gradient. Ecology and Evolution, 11(3), 1378. https://doi.org/10.1002/ece3.7142
- Gould, P. R., Gade, M. R., Wilk, A. J., & Peterman, W. E. (2022). Short-term responses of riparian salamander populations to wildfire in the Southern Appalachians. The Journal of Wildlife Management, 86(7), e22282. https://doi.org/10.1002/jwmg.22282