Effects of soft soap and abamectin on the two spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) and predatory mite Phytoseiulus persimilis A-H (Acari: Phytoseiidae) under laboratory conditions

Abstract

Soft soap at three dosages (3 ml/L, 5 ml/L and 7 ml/L) and abamectin (12.5 mg/100L) were applied to bean plants determine their residual effects on the predatory mite, Phytoseiulus persimilis A-H (Acari: Phytoseiidae) later released for the control of the two-spotted spider mite (TSSM), Tetranychus urticae Koch (Acari: Tetranychidae) under laboratory conditions. The contact toxicity of soft soap and abamectin were evaluated and classified according to IOBC(International Organization for Biological Control) standards. The soap at 3 ml/L and 5 ml/L did not supress TSSM populations and could not provide satisfactory control when compared with soap at 7ml/L and abamectin. The efficacy of soap at 5 ml/L with P. persimilis gave sufficient control of TSSM when compared with soap at 3 ml/L with P. persimilis, and the predator alone. Both the soap at 7 ml/L and abamectin in combination with the predatory mite gave satisfactory control of TSSM ,but in the abamectin treatment, the predatory mite population was not observed due to harmful effects of abamectin. However, use of soft soap at suitable dosage, with or without predatory mite, gave encouraging results for controlling TSSM but was moderately toxic at 5 ml/L and 7 ml/L P. persimilis in contact toxicity testing by causing 50.0 % and 42.3 % mortality, respectively, to adulst of P. persimilis. In addition, abamectin at 12.5 and 25 mg/L (ppm) dosages was evaluated as harmful (T) to adults of P. persimilis. Separately, soft soap caused no phytotoxicity to host plants. However, its phytotoxicity needs to be further investigated under greenhouse and field conditions.