Toxicity, joint action effect, and enzymatic assays of abamectin, chlorfenapyr, and pyridaben against the two-spotted spider mite Tetranychus urticae

Abstract

Background: In the present study, the comparative toxicity of three different acaricides (abamectin, chlorfenapyr, and pyridaben) in technical and formulated forms was assessed on the eggs and adult females of a susceptible strain of Tetranychus urticae. Joint toxic effects of the tested acaricides were also performed against eggs and adults. In addition, the in vitro assay of the tested acaricides was evaluated against some target enzymes isolated from the adult females. Results: The LC 50 values against eggs by leaf-disk-dip technique were estimated to be 294.27, 1032.93, and 9550.54 mg/L for abamectin, chlorfenapyr, and pyridaben, respectively. However, the LC 50 values were 783.06, 666.55, and 731.36 mg/L for the formulations Agromectin, Challenger, and Sanmite, respectively. Abamectin was found to be the greatest lethal to the adults (LC 50 = 5.39 mg/L) followed by chlorfenapyr (LC 50 = 106.51 mg/L) after 24 h of the treatment by slide-dip technique. Pyridaben was least toxic (LC 50 = 690.23 mg/L). Agromectin (LC 50 = 0.94 mg/L) followed by Challenger (LC 50 = 73.65 mg/L) while the Sanmite was the lowest toxic one (LC 50 = 1160.60 mg/L) against the adults. The results of joint toxic action proved that all combinations between the technical or formulated acari-cides exhibited potentiation effect and the toxicity was increased significantly against eggs and adults of T. urticae compared to the individual pesticide. The activity of acetylcholinesterase (AChE), adenosine triphosphatase (ATPase), acid and alkaline phosphatases (ACP and ALP), carboxylesterase (CaE), gamma-aminobutyric acid transaminase (GABA-T), and glutathione-S-transferase (GST) isolated from adults treated with 0.025, 0.05, 0.1, 0.5, 1, and 5 mg/L were significantly inhibited compared to the control. Conclusion: This study provides the theoretical basis for a rational application of abamectin, chlorfenapyr, and pyridaben mixtures in T. urticae control.