Acaricidal Activity and Synergistic Effect of Thyme Oil Constituents against Carmine Spider Mite (Tetranychus Cinnabarinus (Boisduval)).

Lipeng Wu,Xin Huo,Xiaolong Zhou,Duoyong Zhao,Ting Feng,Weizhong He,Shenghong Liu,Cheng Wang,Hejiang Liu

doi:10.3390/molecules22111873

Abstract

Studies examining the use of essential oils as replacements for synthetic insecticides require an understanding of the contribution of each constituent present, interactions among these components, and how they relate to overall toxicity. In the present study, the chemical composition of commercial thyme oil was identified by gas chromatography-mass spectrometry. Thyme oil and blends of its major constituents were tested for their acaricidal activitities against carmine spider mites (Tetranychus cinnabarinus (Boisduval)) using a slide-dip bioassay. Natural thyme oil showed greater toxicity than any single constituent or blend of constituents. Thymol was the most abundant component (34.4%), and also possessed the strongest acaricidal activity compared with other single constituents. When tested individually, four constituents (linalool, terpinene, p-cymene and carvacrol) also had activity, while α-pinene, benzoic acid and ethyl gallate had almost no activity. The toxicity of blends of selected constituents indicated a synergistic effect among the putatively active and inactive constituents, with the presence of all constituents necessary to reach the highest toxicity. The results indicated that thyme oil and some of its major constituents have the potential to be developed into botanical acaricides.

Highlights

Worldwide, an estimated 5% of agricultural production losses are caused by various species of spider mites
In our previous screening program for acaricidal activity of over fifty commercial essential oils, we found that thyme oil possessed the strongest toxicity against T. cinnabarinus
GC-MS analysis identified 12 different compounds, which accounted for 97.8% of the total chemical composition of the thyme oil sample tested (Table 1)

Summary

Introduction

An estimated 5% of agricultural production losses are caused by various species of spider mites. The carmine spider mite Tetranychus cinnabarinus (Boisduval), in particular, has long been recognized as one of the most notorious of tetranychid mites This species have been shown to cause serious damage to the quality and yield of many crops, fruits and vegetables grown in the field or in greenhouse all over the world by damaging foliar tissues, reducing photosynthetic activity and even causing leaf abscission when severe infestations occur [1,2]. The frequent use of these non-selective synthetic pesticides has been shown to have adverse effects on both the environment and human health [8,9], and been linked to mortality of beneficial natural enemies of the mites, resulting in a resurgence of mite populations These problems with increasing levels of resistance to conventional acaricides have led to applications of more frequent and higher doses of insecticides, which further increase the risk to humans and the environment [10]. Studies examining alternatives to traditional chemical treatments such as botanical acaricides that have lower mammalian and environmental toxicity, are being performed [11]

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