Toxicity of Six Commercial Pesticide Formulations to Larvae of Two Tropical Frogs, Rhinella (Bufo) marina (Bufonidae) and Engystomops (Physalaemus) pustulosus (Leptodactylidae)

Azad Mohammed, Nicole Sookoo a

Abstract

Pesticides are non-selective toxicants that can cause significant mortalities in nontarget species such as amphibian. The acute toxicity of three commercial herbicide formulations (Roundup Ultra, Gramoxone Super, Karmex) and three commercial insecticide formulations (Revelo 350CS, Evisect S, BPMC) was determined for larvae of two tropical frog species, Engystomops pustulosus (Leptodactylidae) and Rhinella marina (Bufonidae). The 96 h LC50 for E. pustulosus ranged between 0.3 mg L-1 (Karmex) and 560 mg L-1 (Relevo 350CS) while for R. marinus it ranged between 0.8 mg L-1 (Evisect S) and 280 mg L-1 (Gramoxone Super) following exposure in the aqueous phase alone. Roundup was the only formulation in which LC50 did not vary significantly between the two species. In the presence of soil, the 96 h LC50 for E. pustulosus ranged between 0.8 mg L-1 (Evisect S) and 240 mg L-1 (Relevo 350CS), while the valued for R. marinus ranged between 1.4 mg L-1 (Karmex) and 620 mg L-1 (Relevo 350CS). Engystomops pustulosus was found to be less resistant to the pesticides in the aqueous phase alone, when compared to Rhinella marina. Since both responses varied, lit is unlikely that data collected for anyone species can be used to predict the toxicological responses in another species.