Effects of Dimethoate on Tree Frog (Hyla arborea) Larvae


Abstract: Considering the global decline of amphibian populations, the present study aimed to investigate the sensitivity of tree frogs to a common pesticide, dimethoate. Our study reports the effects of dimethoate on 21^{st}- and 25^{th}-stage Hyla arborea larvae under standardized laboratory conditions in an acute toxicity test using the static system. Specimens used for testing were obtained from the eggs of mating pairs collected at a local natural pond. Each experimental group contained 10 healthy larvae exposed to 5 different concentrations of technical grade dimethoate for 96 h. For each concentration, including the controls, 3 replicates were used. The concentrations of dimethoate causing 50% mortality (LC_{50}) after 96 h were estimated using a probit analysis program. Regarding the lethal concentrations, 21^{st}-stage larvae were more sensitive (LC_{50} = 20.27 ppm) than the 25^{th}-stage larvae (LC_{50} = 37.37 ppm). Malformations such as edema and tail deformaities were observed in 21^{st}- and 25^{th}-stage larvae, respectively. Retardation of growth was also observed in dimethoate-exposed 21^{st}-stage larvae. Certain signs of toxicity, such as initial hyperactivity symptoms, followed by loss of balance, motionlessness, and finally death, were observed.

Keywords: Acute toxicity, organophosphorus pesticides, dimethoate, Amphibia, Hyla arborea, anuran larvae

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