PARENT SESSION
PW1 - Molecular/ Cellular Toxicology
Wednesday, 20 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P714) The Phenylpyrazole Insecticide Fipronil Causes Male Infertility in Meiobenthic Copepods: A Genetic Analysis of Target Loci.

Cary, Tawnya^*,1, Chandler, George¹, Staton, Joseph¹, Coull, Bruce¹, ¹ University of South Carolina, Columbia, SC, USA

ABSTRACT- The GABA disrupting insecticide fipronil is receiving rapidly increased use in the southeastern US in crawfish/rice-culture, turf grass management, and fireant/termite control. Fipronil is highly toxic to estuarine crustaceans, highly lipophilic, and environmentally persistent. A novel 96-well microplate life-cycle bioassay was developed to determine sublethal reproductive and genetic effects of fipronil exposure on the meiobenthic copepod, Amphiascus tenuiremis. This bioassay tracks individual development from the juvenile stage to adult and allows explicit pair mating. Additionally, this approach provides an ideal means for exposing/rearing individuals for endocrine and genetic analyses. Fipronil was evaluated for developmental, reproductive and genetic endpoints. Stage-I copepodites were reared individually to mature adults in 200L solutions containing 0, 0.36, 0.6, or 1.5 ng/mL fipronil. Individuals were checked daily for developmental delays, development of secondary sex characteristics, and time in days to reproductive adult. On day 12, individual pairs of virgin males and virgin females from within each treatment group were transferred to fresh microwells containing the same treatment solution and allowed to mate for 12 days. Viable/non-viable embryo production was recorded for each pair. At the lowest exposure treatment, fipronil caused a 77% reduction in reproductive success as well as a 4 day delay in time from mating to brood sac extrusion compared to controls. Subsequently, when non-successful fipronil-reared females were secondarily mated with control males in clean seawater for an additional 6 days, reproductive success increased by 55%, 60%, and 84%, respectively across treatments. To determine which genes possibly confer fipronil resistance in copepods, reverse transcriptase and PCR techniques have successfully identified a DNA band of comparable size to the GABA receptor gene known to confer cyclodiene resistance in insects.

Key words: fipronil, copepods, life-cycle bioassay, genetic structure