Toxicity of Bacillus thuringiensis israelensis and deltamethrin in three anuran species

Insecticides aid in eliminating crop pests and mosquito-borne diseases but can harm non-target organisms. The insecticidal Gram-positive soil bacterium Bacillus thuringiensis israelensis (Bti) produces toxic proteins that are effective against dipteran insects, such as mosquitoes and black flies. Deltamethrin is an insecticide used to eliminate various invertebrates due to its neurotoxic properties. Despite their widespread use, there is limited toxicity data for these insecticides on nontarget organisms, especially amphibians. Median lethal concentrations (LC₅₀) of Bti and deltamethrin products for three North American amphibian species were determined. Chorus frog (Pseudacris maculata), leopard frog (Lithobates pipiens), and wood frog (Lithobates sylvaticus) tadpoles were exposed to VectoBac® 200G and deltamethrin for 96 h. The LC₅₀ values for VectoBac® 200G were estimated to be 513,000 ± 1.15, 78,860 ± 1.10, and 525,363.4 ± 1.13 ITU/L for chorus, leopard, and wood frog tadpoles, respectively. The LC₅₀ values for deltamethrin were estimated to be 2.69 ± 1.06, 7.30 ± 1.05, and 1.15 ± 1.06 μg a.i./L for chorus, leopard, and wood frog tadpoles, respectively. High concentrations of VectoBac® 200G may cause mortality, whereas low concentrations of deltamethrin induced mortality in all species. Tadpole growth was unaffected, except at high concentrations. These LC₅₀ values and data from literature were used to construct species sensitivity distributions (SSDs) of Bti and deltamethrin products. Analysis of SSDs revealed that amphibian species were relatively tolerant of Bti products and susceptible to deltamethrin exposure.