Relyea found that a mixture of all 10 chemicals killed 99 percent of Leopard Frog tadpoles as did the insecticide-only mixture; the herbicide mixture had no effect on the tadpoles. While Leopard Frogs perished, Gray Treefrogs did not succumb to the poisons and instead flourished in the absence of Leopard Frog competitors. Relyea also discovered that endosulfan—a neurotoxin banned in several nations but still used extensively in U.S. agriculture—is inordinately deadly to Leopard Frog tadpoles. By itself, the chemical caused 84 percent of the Leopard Frogs to die. This lethality was previously unknown because current regulations from the U.S. Environmental Protection Agency (EPA) do not require amphibian testing, Relyea said. His results showed that endosulfan was not only highly toxic to leopard frogs, but also that it served as the linchpin of the pesticide mixture that eliminated the bulk of leopard frog tadpoles.