The insecticidal and repellent activities of the four wild plant extracts: stinging nettle, Urtica dioica L., white henbane, Hyoscyamus albus L., camphorweeds, Pluchea dioscoridis L., and cocklebur, Xanthium strumarium L. were tested compared to the insecticide spirotetramat against the 3rd nymphal instar of Aphis gossypii Glover and adult females of Phenacoccus solenopsis Tinsley after 24 and 48 h of treatment. Their effects on acetylcholinesterase (AChE) and glutathione-S-transferase (GST) enzyme activities were also assessed to explore their possible mechanisms of action. The phenolic compounds of the plant extracts were investigated by high-performance liquid chromatography (HPLC) analysis. The most abundant compounds in the methanol extract from P. dioscoridis were gallic acid (14.45 µg/mL), and cinnamic acid (11.44 µg/mL); from U. dioica were caffeic acid (15.32 µg/mL) and syringic acid (13.47 µg/mL); from H. albus were syringic acid (7.12 µg/mL) and catechol (5.33 µg/mL); and from X. strumarium were p-coumaric acid (24.53 µg/mL) and pyrogallol (18.35 µg/mL). According to the LC50 values, the contact toxicity of U. dioica, H. albus, P. dioscoridis, and X. strumarium against A. gossypii was 40.3, 60.6, 56.2, and 32.3 mg/L, whereas, the contact toxicity against P. solenopsis was 56.4, 67.5, 64.3, and 36.2 mg/L, compared to the spirotetramat (17.2 and 24.5 mg/L), respectively, at 48 h of treatment. The highest repellency rates were observed with LC50 values for X. strumarium (63.2 and 60.3%), followed by U. dioica (46.2 and 43.5%), P. dioscoridis (45.3 and 42.8%), and H. albus extract (38.8 and 35.2%) compared to the spirotetramat (78.5 and 76.2%) against A. gossypii and P. solenopsis at 24 h, but decreased with time. The AChE and GST activities in pests were significantly inhibited, compared to control and spirotetramat, with dose and time-dependent effects. These findings indicate that tested wild extracts may be suggested as viable alternatives for aphids and mealybugs control.
