Fipronil effects on estuarine copepod (Amphiascus tenuiremis) development, fertility, and reproduction: A rapid life-cycle assay in 96-well microplate format

Authors

  • G. Thomas Chandler,

    Corresponding author
    1. Department of Environmental Health Sciences, Arnold School of Public Health, University of South Carolina, Columbia, South Carolina 29208, USA
    • Department of Environmental Health Sciences, Arnold School of Public Health, University of South Carolina, Columbia, South Carolina 29208, USA
    Search for more papers by this author
  • Tawnya L. Cary,

    1. Department of Environmental Health Sciences, Arnold School of Public Health, University of South Carolina, Columbia, South Carolina 29208, USA
    Search for more papers by this author
  • David C. Volz,

    1. Department of Environmental Health Sciences, Arnold School of Public Health, University of South Carolina, Columbia, South Carolina 29208, USA
    Search for more papers by this author
  • Spencer S. Walse,

    1. Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, USA
    Search for more papers by this author
  • John L. Ferry,

    1. Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, USA
    Search for more papers by this author
  • Susan L. Klosterhaus

    1. Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, Solomons, Maryland 20688, USA
    Search for more papers by this author

Abstract

Fipronil is a novel γ-aminobutyric acid receptor-specific phenylpyrazole insecticide commonly used near estuarine environments for rice production, turf-grass management, and residential insect control. In this study, we evaluated the acute, developmental, and reproductive toxicity of fipronil to the estuarine harpacticoid copepod Amphiascus tenuiremis. Fipronil was highly toxic to A. tenuiremis (adult 96-h median lethal concentration [LC50] = 6.8 μg/L) and was more toxic to male copepods (96-h LC50 = 3.5 μg/L) than to nongravid female copepods (96-h LC50 = 13.0 μg/L). By using a newly developed 96-well microplate-based life-cycle toxicity test, we successfully reared single individuals of A. tenuiremis to adulthood in 200-μl microwells and concurrently assessed developmental and reproductive effects (after paired virginal matings) of environmentally relevant aqueous fipronil concentrations (0.16, 0.22, and 0.42 μg/L measured). Throughout the entire life cycle, copepod survival in all treatments was >90%. However, fipronil at 0.22 μg/L and higher significantly delayed male and female development from stage 1 copepodite to adult by approximately 2 d. More importantly, fipronil significantly halted female egg extrusion by 71% in the 0.22-μg/L fipronil treatment, and nearly eliminated reproduction (94% failure) in the 0.42-μg/L fipronil treatment. A three-generation Leslie matrix-based population growth model of fipronil reproductive and life-cycle impacts predicted a 62% decline in population size of A. tenuiremis relative to controls at only 0.16 μg/L.

Ancillary