Effects of a mixture of vegetable and essential oils and fatty acid potassium salts on Tetranychus urticae and Phytoseiulus persimilis.

Laboratory trials were carried out to evaluate the toxicity and the influence of a commercial mixture of vegetal, essential oils, andpotassium salts of fatty acids (Acaridoil 13SLs) on the population growth rate (ri—instantaneous rate of increase) of two mite species,the phytophagous Tetranychus urticae Koch and the predator Phytoseiulus persimilis Athias-Henriot. A residue of 1.3 mg/cm2 ofpesticide solution was harmless for Ph. persimilis eggs, while a moderate mortality of eggs and of larvae from treated eggs of T. urticae,was observed (53.8%). The pesticide also caused a delay in the postembryonic development of the tetranychid. Moreover, 83.4%mortality was reported for treated females tetranychids and only 24.0% for Ph. persimilis females. The pesticide influenced negatively thepopulation growth of T. urticae which showed a very low rate of increase (ri ¼ 0.07), compared to that obtained in the control (ri ¼ 0.68).The pesticide did not affect negatively the reproductive potential of Ph. persimilis (ri ¼ 0.54 and ri ¼ 0.57 for test and control,respectively). These results suggest a considerable acaricidal activity of potassium salts of fatty acids and caraway oil on T. urticae and agood selectivity on Ph. persimilis.