Ovicidal and Adulticidal Activity of Eucalyptus globulus Leaf Oil Terpenoids against Pediculus humanus capitis (Anoplura: Pediculidae)

Abstract

The toxic effects of Eucalyptus globulus leaf oil-derived monoterpenoids [1,8-cineole, l-phellandrene, (−)-α-pinene, 2-β-pinene, trans-pinocarveol, γ-terpinene, and 1-α-terpineol] and the known Eucalyptus leaf oil terpenoids (β-eudesmol and geranyl acetate) on eggs and females of the human head louse, Pediculus humanus capitis, were examined using direct contact and fumigation bioassays and compared with the lethal activity of δ-phenothrin and pyrethrum, two commonly used pediculicides. In a filter paper contact bioassay with female P. h. capitis, the pediculicidal activity was more pronounced with Eucalyptus leaf oil than with either δ-phenothrin or pyrethrum on the basis of LT₅₀ values (0.125 vs 0.25 mg/cm²). 1,8-Cineole was 2.2- and 2.3-fold more toxic than either δ-phenothrin or pyrethrum, respectively. The pediculicidal activities of (−)-α-pinene, 2-β-pinene, and (E)-pinocarveol were comparable to those of δ-phenothrin and pyrethrum. l-Phellandrene, γ-terpinene, and 1-α-terpineol were relatively less active than δ-phenothrin and pyrethrum. β-Eudesmol and geranyl acetate were ineffective. 1-α-Terpineol and (E)-pinocaveol were highly effective at 0.5 and 1.0 mg/cm², respectively, against P. h. capitis eggs. At 1.0 mg/cm², (−)-α-pinene, 2-β-pinene, and γ-terpinene exhibited moderate ovicidal activity, whereas little or no ovicidal activity was observed with the other terpenoids and with δ-phenothrin and pyrethrum. In fumigation tests with female P. h. capitis at 0.25 mg/cm², 1,8-cineole, (−)-α-pinene, (E)-pinocarveol, and 1-α-terpineol were more effective in closed cups than in open ones, indicating that the effect of the monoterpenoids was largely due to action in the vapor phase. Neither δ-phenothrin nor pyrethrum exhibited fumigant toxicity. Eucalyptus leaf oil, particularly 1,8-cineole, 1-α-terpineol, and (E)-pinocaveol, merits further study as potential pediculicides or lead compounds for the control of P. h. capitis. Keywords: Natural insecticide; pediculicide; ovicide; fumigant; Pediculus humanus capitis; human head louse; Eucalyptus globulus; 1,8-cineole; α-terpineol; (E)-pinocaveol; monoterpenoid