Biological activity and safety evaluation of monoterpenes against the peach aphid ( Myzus persicae Sulzer) (Hemiptera: Aphididae)

The green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), is an economically important cosmopolitan crop pest. Essential oils (EOs) are complex mixtures of secondary metabolites that exhibit a wide range of biological activities, including antioxidant, antimicrobial and anti-inflammatory activities. Monoterpenes, as the major constituents of EOs, are well known for having a range of biological activities. In this study, 9 monoterpenes were screened for fumigant toxicity against M. persicae , and the safety of monoterpenes to natural enemies was evaluated. The results of the bioassays indicated that 9 monoterpenes showed promising fumigant toxicity against M. persicae . Carvacrol was the most toxic compound based on the LC 50 value, which was 1.566 mg/L, followed by bornyl acetate, terpinolene, and terpinyl acetate, which had higher toxicities towards aphids, with LC 50 values of 2.648 mg/L, 2.759 mg/L, and 2.832 mg/L, respectively. In addition, the safety evaluation assays of carvacrol against Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) larvae (LC 50 = 43.851 mg/L) did not affect nontarget invertebrates at concentrations that effectively controlled aphids. Carvacrol was safer than chlorpyrifos to natural enemy H. axyridis larvae (toxicity ratio = 28.00 > 2.93). These results identified several high-activity monoterpenes that can be used against this pest in greenhouses as botanical insecticides.