THE FUNCTIONAL INTEGRITY OF NORTHERN LEOPARD FROG (RANA-PIPIENS) AND GREEN FROG (RANA-CLAMITANS) POPULATIONS IN ORCHARD WETLANDS - II - EFFECTS OF PESTICIDES AND EUTROPHIC CONDITIONS ON EARLY-LIFE STAGE DEVELOPMENT

Premetamorphic northern leopard frogs (Rana pipiens) and green frogs ( Rana clamitans) were evaluated at seven wetland sites, four of which w ere within apple orchards, to determine if environmental conditions as sociated with orchard management in southern Ontario, Canada, affected frog early development. Synchronous with breeding events (May-July), embryos and tadpoles were exposed, in situ and in the laboratory, to s tudy site pond water for 2 to 3 weeks. Six pesticides commonly applied in apple orchards (Guthion(R) 50WP, Imidan(R) 50WP, Thiodan(R) 50WP, Dithane(R) DG, Nova(R) 40W, and Basudin(R) 500EC) and technical grade diazinon were also evaluated for direct toxicity to green frogs using continuous and discontinuous toxicity tests. Embryos and larvae exhibi ted poor hatching success and survival at some orchard sites during in situ assays, but no specific water source produced consistently poor developmental success. Reduced tadpole growth occurred at several stud y sites, showing no clear distinction between reference and orchard si tes. Despite the collection of substantial environmental data, only su rface water temperature appeared to be correlated with growth rates. B asudin 500EC, technical grade diazinon, and Dithane DG caused mortalit y, deformities, or growth inhibition during early development at envir onmentally relevant concentrations (<0.01 mg/L), whereas Imidan 50WP, Guthion 50WP, and Nova 40W produced survival or growth effects at much higher levels (5-10 mg/L). Dithane DG (mancozeb) was acutely toxic du ring prolonged exposures, and sublethal growth and deformity responses occurred at nominal concentrations greater than 0.01 mg/L. Diazinon w as the most toxic to green frogs, with median lethal concentrations of 2.8 to 5 mu g/L and median effective concentrations of 6 to 14 mu g/L for formulation and technical grades, respectively. The combined resu lts of in situ and laboratory tests of green frog and leopard frog dev elopmental success suggested that embryo-larval development of these t wo species could be accomplished at all study sites, independent of th e association with apple orchards.