Acaricidal activity of Shirazian thyme and rosemary methanolic extracts in combination with spirodiclofen and propargite on Tetranychus urticae (Acari: Tetranychidae)

The two-spotted spider mite, Tetranychus urticae Koch is one of the polyphagous pests that attack a wide range of crops. In recent decades, excessive application of synthetic acaricides has led to its resistance to pesticides and environmental pollution. However, considering the importance of the role of pesticides in controlling plant pests, it is impossible to cease using these compounds. In recent decades, new methods such as the use of plant extracts have been proposed that not only control pests but also have no residues and harmful environmental effects. Also, the use of plant extracts in combination with synthetic pesticides while controlling the pest, reduces the amount of pesticide usage. In this study, the efficacy of methanolic extracts of Zataria multiflora and Rosmarinus officinalis was investigated individually and in combination with spirodiclofen and propargite to control two-spotted spider mites. Bioassay tests were performed using the leaf dipping method. Each treatment was performed in three independent biological replications and the mortality was recorded 24 h after exposure. The 50% lethal dose (LC50) of spirodiclofen and propargite as well as methanolic extracts of Z. multiflora and R. officinalis were estimated to 1.89, 12.76, 1934.13, and 4382.07 mg/l, respectively. In addition, results of experiments related to mixing plant extracts with acaricides showed that the combination of Z. multiflora extract with spirodiclofen and propargite caused a synergistic effect with a co-toxicity coefficient of 66.66 and 55.55, respectively. However, the combination of R. officinalis extract with spirodiclofen and propargite caused an antagonistic response with −77.78 and −80.56, respectively.