Methyl eugenol bioactivities as a new potential botanical insecticide against major insect pests and their natural enemies on rice (Oriza sativa)

The bioactivities of methyl eugenol (ME) against rice insect pests, the brown planthopper (BPH), Nilarparvata lugens, the leaf folder (RLF), Cnaphalocrocis medinalis, the striped stem borer (SSB), Chilo suppressalis, and their major natural enemies, a predator Cyrtorhinus lividipennis and parasitoids Anagrus nilaparvatae and Trichogramma japonicum were determined under laboratory conditions. The results showed ME had repellent, systemic and contact insecticidal activities against BPH. The nymphal mortality increased with raised ME concentrations. The LC50 value for BPH using an impregnated filter paper bioassay was 1025 mg/L which was much lower than that of 3778 mg/L obtained from an immersion bioassay. ME also had a contact toxicity against RLF larvae with a LC50 of 250 mg/L. However, bioactivity of ME against SSB larvae was much lower than against RLF. Only 21.8% of 2nd instar SSB larvae died at 24 h after being treated with 8000 mg/L ME. In addition, ME also had contact toxicity to predator C. lividipennis and parasitic natural enemies A. nilaparvatae, T. japonicum, with LC50 values of 527, 105 and 123 mg/L, respectively. Even so, the toxicity of ME to natural enemies was much lower than that of chemical insecticides.