The lethal, sublethal and developmental effects of the botanical insecticide Margosan-O(RTM) (Azadirachta indica extracts) on wood frogs (Rana sylvatica)

The study examines the relative toxicity of the botanical insecticide, Margosan-O{dollar}spcircler{dollar}, an extract from the Indian Neem plant, Azadirachta indica, to various life-stages, viz. embryos, tadpoles and adults, of a non-target species, the wood frog (Rana sylvatica). Analysis of the experimental data indicate that an exposure of 96h to an estimated median concentration of 1 114.0 mg/L Margosan-O{dollar}spcircler{dollar} is required to block 50% emergence (lethality) in R. sylvatica embryos (96h, LC{dollar}sb{lcub}50{rcub}{dollar}) (Spearman's r = {dollar}-{dollar}0.92). Kruskal - Wallis one-way analysis of variance revealed significant differences (p {dollar}<{dollar} 0.0001) in development between embryos in filtered pond water and those exposed to Margosan-O{dollar}spcircler{dollar}. Post hoc analysis of the data indicate significant differences in embryonic development between treatment groups. Sub-lethal tests conducted with higher developmental stages reveal that the effective median concentration required to illicit "knockdown" of tadpoles after 48h (EC{dollar}sb{lcub}50{rcub}{dollar}) was 180.0 mg/L (Spearman's r = {dollar}-{dollar}0.97), representing a marked decrease in tolerance between R. sylvatica embryos and tadpoles. Margosan-O{dollar}spcircler{dollar} was practically non-toxic up to a concentration of 2 000.0 mg/L for 48h in direct contact to R. sylvatica adults. Although this particular Neem product appears to be relatively "safe" to the life stages tested, it may pose a risk to the development of R. sylvatica.