by Spencer Saunders
Faculty mentor: Dr. Tyler Frankel
Thiamethoxam is a neonicotinoid insecticide that targets the nicotinic acetylcholine receptors of target organisms. It is used on a wide variety of crops and can be applied in multiple methods including seed coatings, broadcast sprays, or foliar sprays. As thiamethoxam is highly soluble, it easily enters aquatic environments and surface water through run-off events from agricultural fields. Detected environmental concentrations have ranged from the low ng/L range up to 225 ug/L. While the effects of thiamethoxam exposure has been well studied in aquatic vertebrates, few studies have examined their impacts on freshwater invertebrates. As such, this study assessed the impacts of thiamethoxam exposure on the viability, behavior, and shell growth of juvenile freshwater bladder snails (Physa acuta). Adult P. acuta specimens were collected from local waterways in Fredericksburg, VA and bred under laboratory conditions for several generations. Laboratory hatched one-week old juveniles were then exposed to various concentrations of thiamethoxam (0 (EtOH control), 1.56, 3.13, 6.25, 12.5, or 25 ug/L) for two weeks using a static replacement exposure method (100% change every four days). Mortality was assessed every 24 hours, while shell growth and behavior were assessed on day 7 and day 14. Photos of each snail were obtained after one and two weeks and growth was measured using ImageJ (v1.8.0). Behavior was assessed using ToxTrac (v2.83) including average speed, average velocity, total distance traveled, and time spent stationary. While this experiment is still ongoing, we expect to see higher mortality rates and decreased growth concurrent with higher concentrations of thiamethoxam. We also expect to see increases in average speed, average velocity, and total distance traveled with increased exposure concentrations. Our findings will help expand our knowledge on how thiamethoxam impacts multiple physiological endpoints of a novel freshwater invertebrate species.