Toxicity of Azadirachta indica Oil at Different Temperatures against Female Tetranychus urticae (Acari: Tetranychidae)

Abstract

Tetranychus urticae Koch (Acari: Tetranychidae) is a polyphagous pest of global agricultural importance, with a high capacity for adaptation and numerous cases of resistance to synthetic acaricides. In response to this problem, botanical products, such as neem oil, represent promising alternatives. This study evaluated the toxicity of neem oil on adult females of T. urticae at 5 temperatures ranging from 23 to 50°C). At commercial doses, the product caused 100% mortality at all temperatures, therefore, a bioassay was conducted to estimate the concentration-mortality response of the mites to the neem extract. These results demonstrated that between 23 and 45°C, there were no significant differences in toxicity, as indicated by overlapping 95% confidence limits of the median lethal concentrations (LC50s). However, at 50°C, toxicity increased markedly, with the lowest LC50 and LC95 values and the highest relative toxicity. This suggests a synergistic effect between thermal stress and mode of action of neem against T. urticae females. Therefore, integrating combined thermal treatments with neem into agricultural systems, especially for crops that tolerate these temperatures, for example, deciduous crops during dormancy or in regions with extreme temperatures, may prove to be a sustainable strategy to reduce the use of synthetic acaricides.