Spread of Red Imported Fire Ant, Solenopsis invicta, in Virginia and effects of sub-lethal exposure to agrochemicals on its behavior
Malone, Morgan Le Fae
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Solenopsis invicta is an invasive ant that has caused detrimental impacts to ecosystems and economies in the Southeastern United States, recently including Virginia. In this study, we explored the invasion ecology of S. invicta through two main objectives. First, we established a comprehensive distribution map of S. invicta in Virginia through multiple survey techniques. We then compared our findings with published models quantifying the potential spread of S. invicta and created our own species distribution model. In 2020-2021, S. invicta occurrences were found in 7 counties beyond the current Quarantine and our data show that S. invicta has spread further than predicted. Our own species distribution model suggests that the distribution area for S. invicta is likely to increase under the projected climate change. This study provides insights into the range expansion of S. invicta at the border of its suitable habitat and allow for improvements to models of its spread under these conditions. Additionally, it provides useful information to inform county extension agents to know where they are to expect new infestations of S. invicta. Second, we investigated the impacts of pesticide residue on the behavior of S. invicta through neonicotinoid exposure. We found detectable levels of neonicotinoids in the soil of the ant mounds as well as in the ants themselves. In addition, we investigated the effects of dietary exposure to imidacloprid on foraging behavior in a laboratory setting. We found that unexposed colonies were able to locate the food source more quickly during the second trial while exposed ants were unable to improve their performance. We also found that more exposed ant workers were unable to successfully navigate the maze as compared to unexposed workers. Our results suggest impaired learning of maze tasks and impaired navigational skills in neonicotinoid-exposed ants.
General Audience Abstract
The red imported fire ant (RIFA) is an invasive ant species found throughout the Southeastern United States that has negatively impacted ecosystems and economies. In the past few decades, RIFA has invaded the Coastal Plain of Virginia, resulting in legislation that restricts the movements of soil, plant products, and some equipment in and out of several southeastern counties and independent cities. To develop better management practices, there is a critical need to understand the spread, establishment, and impacts of RIFA in greater detail. We aimed to do this by surveying the current distribution of RIFA in Virginia and investigate the impact of insecticide use on their spread and behavior. In 2020-2021, we found RIFA occurrences in 7 counties beyond the current Quarantine, which is further than previously predicted. We then built a model using climatic variables that predicts the distribution of RIFA and found their habitable range is likely to increase under the projected climate change. Additionally, we investigated the impacts of common agricultural pesticides on the behavior of RIFA. We found these chemicals present in both the soil of the ant mounds and in the ants themselves. We also found that dietary exposure to imidacloprid, a neonicotinoid pesticide, altered the foraging behavior of RIFA. This study provides useful information to advise county extension agents to know where they are to expect new infestations of RIFA. Our results also suggest that human activity alters the invasion ecology of recent arrivals such as the red imported fire ant.
- Masters Theses