Behavioral Responses, Fumigant Toxicity, and Contact Toxicity of Eugenol and Cinnamaldehyde Against Sitobion avenae Under Controlled Conditions

Traditionally, the control of Sitobion avenae (Fabricius) relies heavily on chemical insecticides; however, the long-term use of chemical insecticides has caused hazards to the environment and human health. Eugenol and cinnamaldehyde are important active components of plant essential oils. In this study, the toxicity of these two compounds against S. avenae was determined via fumigation and contact bioassays, and repellent activity tests were conducted to clarify their control effects. The results showed that the contact KD50 values of eugenol and cinnamaldehyde against S. avenae through cuticular penetration were 0.25 μL/mL and 0.11 μL/mL, respectively (applied onto a treated surface area of 30 cm2 per replicate), while their fumigant KD50 values were 7.04 μL/mL and 2.55 μL/mL, respectively (tested in a sealed 125 mL glass vial). Both compounds exhibited repellent activity. At a concentration of 0.75 μL/mL, the repellency rate of cinnamaldehyde was 24.4%, while that of eugenol was 15.6%. However, both compounds displayed a certain attractive effect at the lowest concentration of 0.375 μL/mL. These findings demonstrate that eugenol and cinnamaldehyde exhibit high insecticidal activity against the wheat aphid under laboratory conditions, with dose-dependent repellency and toxicity in simple laboratory assays.