Persistence of Toxicity in Four Natural Extracts Controlling Tetranychus urticae as Affected by Tween®20 Supply

Abstract

Natural plant extracts are considered as promising tools to fight pests such as phytophagous mites and particularly against Tetranychus urticae that causes damage of economic importance in agriculture. The aim of the present work was to analyze the persistence of their biocidal activity and to investigate the possibility of extending their activities against T. urticae. Three essential oils from Deverra scoparia, Hertia cheirifolia and Santolina africana, and one distillate from Allium sativum are effective in controlling the two spotted spider mite T. urticae. The persistence of the plant extracts was evaluated and compared with and without a non-ionic surfactant composed of monosorbitanoleate (Tween®20). Without Tween®20 and five days following treatment, the four extracts rapidly lost their toxicity against T. urticae indicating low persistence of their biological activity. With Tween®20, their persistence significantly increased and lasted 10 days. The combination with Tween®20 significantly increased the differences between the respective persistence of the four plant extracts with S. africana being the most persistent extract and D. scoparia the less persistent. Even if possessing a high toxicity against T. urticae, natural plant extracts have only a poor persistence of their toxic effect. The enhancement of their efficacy and the increase of their persistence achieved by the use of Tween®20 make them a promising tool for pest management of the two spotted spider mite T. urticae.

Keywords

• Extracts
• persistence
• pest management
• plant extracts
• Tetranychus urticae
• Tween®20