Efficacy of Spray Formulations Containing Binary Mixtures of Clove and Eucalyptus Oils Against Susceptible and Pyrethroid/Malathion-Resistant Head Lice (Anoplura: Pediculidae)

The control efficacy of clove, Eugenia caryophyllata, and eucalyptus, Eucalyptus globulus, essential oils and 15 formulations containing these essential oils alone (8, 12, and 15% sprays) and their binary mixtures (7:3, 5:5, and 3:7 by weight) against adult females of insecticide-susceptible KR-HL and dual malathion- and permethrin-resistant BR-HL strains of head louse, Pediculus humanus capitis (De Geer), was examined by using contact plus fumigant and human hair wig (placed over the head of mannequin) mortality bioassays. In contact plus fumigant mortality bioassay, essential oils from eucalyptus (0.225 mg/cm(2)) and clove (1.149 mg/cm(2)) were less effective than either d-phenothrin (0.0029 mg/cm(2)) or pyrethrum (0.0025 mg/cm(2)) based on 6-h median lethal concentration values. However, the efficacies of eucalyptus and clove oils were almost identical against females from both strains, despite high levels of resistance of the BR-HL females to d-phenothrin (resistance ratio, 667) and pyrethrum (resistance ratio, 754). In human hair wig mortality bioassay, eucalyptus oil spray treatment gave better control efficacy than either spray treatment with clove oil alone or their binary mixtures. Thus, eucalyptus applied as 8% sprays (15 or 20 ml) appears to provide effective protection against pediculosis even to insecticide-resistant head louse populations. Once the safety issues resolved, covering the treated hair and scalp with bath shower cap or hat would ensure the fumigant action of the essential oil.