Clothianidin Exposure Associated with Changes in Tadpole Behavior

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During a laboratory exposure study, tadpole movement decreased with increased concentrations of clothianidin, a neonicotinoid pesticide. Decreased movement could affect a tadpole’s ability to forage, escape predation, and metamorphose before ponds dry.

Southern Leopard Frog

Southern Leopard Frog (Credit: Gabriel Kamener. Public domain.)

Neonicotinoids, a class of insecticides used for pest control on a variety of crops, persist in water and soils, are easily transported in the environment, and have been detected in surface waters throughout the United States. Amphibians using surface waters during various life stages could be exposed to these contaminants and may be more susceptible to dermal exposure than other species owing to their highly permeable skin. Little is known about the potential effects of neonicotinoid exposure on animals other than insects, such as amphibians, and clothianidin currently is under registration review at the U.S. Environmental Protection Agency. Therefore, scientists evaluated the sublethal effects of the neonicotinoid clothianidin on the behavior of southern leopard frog tadpoles (Rana sphenocephala).

Scientists from the U.S. Geological Survey (USGS) and academia completed a laboratory study exposing 500 tadpoles to clothianidin in a  for 96 hours at six different environmentally-relevant concentrations. The scientists assessed measures of tadpole movement for 1 hour post-exposure and measured total displacement, mean velocity, maximum velocity, and time spent moving.

The survival rate of the tadpoles was 99 percent after 96 hours of exposure; however, additional testing demonstrated that exposed tadpoles generally moved less distance, moved more slowly, and spent less time moving. Two of the measures, total displacement and mean velocity, had a strong negative association with clothianidin exposure concentration.

USGS Scientist collecting a water-quality sample from the South Fork Zumbro River, MN

Neonicotinoids have been detected in surface waters throughout the United States. (Credit: Donald S Hansen, U.S. Geological Survey. Public domain.)

This laboratory study demonstrated that exposure to neonicotinoids can slow tadpole behavioral responses, even at environmentally relevant, sublethal concentrations. These findings could indicate that amphibian exposure to clothianidin in the environment could affect a tadpole’s ability to forage, escape predation, and metamorphose before ponds dry. This study adds to the growing body of evidence that there can be sublethal effects of neonicotinoid insecticides on non-target organisms.

This research was funded by the USGS Ecosystems Mission Area; the USGS Environmental Health Program (Toxic Substances Hydrology and Contaminant Biology); the University of Missouri College of Agriculture, Food, and Natural Resources; and the Missouri Cooperative Fish and Wildlife Research Unit, which is jointly sponsored by the Missouri Department of Conservation, the University of Missouri, the U.S. Fish and Wildlife Service, and the Wildlife Management Institute.