Journal of Taiwan Agricultural Research

Author:Jih-Zu Yu* and Bing-Huei Chen

Abstract:

    Effects of three vegetable oils including coconut oil, palm oil and rapeseed oil on two-spot spider mite (Tetranychus urticae Koch) were examined under laboratory conditions (25℃ ± 1℃).  Nonionic surfactants were prepared using Span 80 and Tween 80.  The hydrophile-lipophile balance (HLB) values were adjusted to 5.3, 10.8 and 6.7 and mixed with coconut oil, palm oil and rapeseed oil, respectively, at the ratio of 1 : 1 (V/V) to prepare emulsified solutions.  Each of the emulsions was diluted with distilled water to the oil concentrations of 20, 10, 5, 2.5 and 1.25 mL/L and then used for the experiments.  The surfactant used in each vegetable oil was also diluted to 20, 10, 5, 2.5 and 1.25 mL/L and used as controls.  Results showed that among the three vegetable oil emulsions tested, coconut oil and palm oil were acaricidal on T. urticae.  After treatment for 72 h, the LC₅₀ for coconut oil and palm oil was 2.23 and 2.59 mL/L, respectively and the LC₉₀ was 10.62 and 7.53.  The acaricidal effect seemed to be related to high saturated fatty acid content in the coconut and palm oils.  Acaricidal function of surfactants was unaffected by HLB-value excepted for the concentrations of 10 mL/L at 24 h after treatment and 20 mL/L at 72 h after treatment.  Results of this study also showed that the three surfactants at HLB-values of 5.3, 10.8 and 6.7 were acaricidal on T. urticae.  This study suggests that coconut oil and palm oil may be of potential for use in the formulation of acaricides for control of T. urticae.

Key words:Tetranychus urticae, Coconut oil, Palm oil, Rapeseed oil, HLB-value of surfactant

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