Efficacy of three elicitors on Tetranychus urticae Koch (Acari: Tetranychidae) infestation level and its associated natural enemies on Phaseolus vulgaris L. and their effects on plant parameters

Three basic phenolic elicitors (acetylsalicylic (Aspirin), benzoic and salicylic acids) at the rate of approximately 0.01 mol/l of each (i.e. 1.8, 1.25, and 1.4 g/l, respectively) were applied as a dry bean for reducing Tetranychus urticae Koch (Acari: Tetranychidae) infestation level and some of its natural enemies. Potassium carbonate (0.75 g/l) was added as a dissolver. The experiment was conducted over two consecutive years 2019–2020 under open field conditions. Elicitors were applied fortnightly four times over the vegetative growth stage. The application started 15 days after the sowing date. Results showed that tested elicitors reduced T. urticae females’ population by 32.10, 36.94, and 25.43%, respectively compared with the control. These reductions were not efficient to be considered as pesticides. Aspirin and benzoic were superior to salicylic. Densities of four associated predators were not generally affected. The three elicitors significantly enhanced the leaves' contents of chlorophyll A & B, nitrogen%, phosphorous%, potassium%, and total phenol. They increased the mean plant growth parameters by 56.71, 44.99, and 4.53%, respectively. This was reflected in seeds' estimated yield/plant increase by 134.7, 135.6, and 22.2%, respectively compared with the control with generally insignificant chemical components compared to control. Associated mite predator populations (i.e. Chrysoperla carnea, Phytoseiulus persimilis, Orius insidiosus Scolothrips sexmaculatus) were similar to control ones. More efforts are suggested in this manner to improve productivity at a lower cost and environmentally friendly.