Ovicidal and Adulticidal Effects of Eugenia caryophyllata Bud and Leaf Oil Compounds on Pediculus capitis

The toxicity of Eugenia caryophyllata bud and leaf oil-derived compounds (acetyleugenol, β-caryophyllene, eugenol, α-humulene, and methyl salicylate) and congeners of eugenol (isoeugenol and methyleugenol) against eggs and females of Pediculus capitis was examined using direct contact application and fumigation methods and compared with those of the widely used δ-phenothrin and pyrethrum. In a filter paper diffusion bioassay with female P. capitis, the pediculicidal activity of the Eugenia bud and leaf oils was comparable to those of δ-phenothrin and pyrethrum on the basis of LT50 values at 0.25 mg/cm2. At 0.25 mg/cm2, the compound most toxic to female P. capitis was eugenol followed by methyl salicylate. Acetyleugenol, β-caryophyllene, α-humulene, isoeugenol, and methyleugenol were not effective. Eugenol at 0.25 mg/cm2 was as potent as δ-phenothrin and pyrethrum but was slightly less effective than the pyrethroids at 0.125 mg/cm2. Against P. capitis eggs, methyl salicylate and eugenol were highly effective at 0.25 and 1.0 mg/cm2, respectively, whereas little or no activity at 5 mg/cm2 was observed with the other test compounds as well as with δ-phenothrin and pyrethrum. In fumigation tests with female P. capitis at 0.25 mg/cm2, eugenol and methyl salicylate were more effective in closed cups than in open ones, indicating that the effect of the compounds was largely due to action in the vapor phase. Neither δ-phenothrin nor pyrethrum exhibited fumigant toxicity. The Eugenia bud and leaf essential oils, particularly eugenol and methyl salicylate, merit further study as potential P. capitis control agents or lead compounds. Keywords: Natural insecticide; pediculicide; ovicide; fumigant; Pediculus capitis; Eugenia caryophyllata; essential oil; GC-MS; eugenol; methyl salicylate; mode of action