Distribution of frogs in rice bays within an irrigated agricultural area : links to pesticide usage and farm practices

The occurrence of four frog species in rice bays of the Coleambally Irrigation Area (NSW, Australia) was studied over two seasons. The mean abundance of Litoria raniformis tadpoles was significantly lower in the northern sites compared to the southern sites. In contrast, tadpoles of the three other species had a uniform distribution across all study sites. A discriminant analysis showed low concentrations of the corn herbicide metolachlor and increased pH were the main variables studied that determined site occupation by L. ranifromis. We concluded that farm practices associated with increased corn cropping in the northern region, rather than any direct effect of corn herbicides, determine the reduced species presence of L. raniformis in the northern region.