STRUCTURE-BIOACTIVITY RELATIONSHIPS AMONG ESSENTIAL OIL COMPONENTS AGAINST HUMAN LICE PEDICULUS HUMANUS CAPITIS (ANOPLURA: PEDICULIDAE)

TOLOZA. A.C.; MOUGABURE CUETO G. A.; ZYGADLO J.; ZERBA E. AND PICOLLO M.I.

Montevideo, Uruguay.

Congreso; V Reunión de la Sociedad Latinoamericana de Fotoquímica “Prof. Emer. Patrick Moyna”. I Congreso de Fitoterápicos del Mercosur.; 2005

The infestation with the ectoparasite Pediculus humanus capitis is a worldwide problem affecting most of the children 5-12 yr old, in both developed and development countries. The repetitive employment of conventional insecticides during past decades, such as permethrin has resulted in the development of resistance to this product (1). The use of natural products like the essential oils is an interesting alternative to permethrin because they are environmental friendly and not acutely toxic to mammals (2). The purposes of the present study were to evaluate the vapor activity of twenty one essential oil components against permethrin-resistant head lice from Buenos Aires, and to determine structure-pediculicidal activity relationships among effective essential oil components. Head lice were collected from heads of infested children 6-12 yr old, using a fine toothed antilouse comb. The tested essential oil constituents were: anethole,  anisole, benzyl alcohol, borneol, camphor, carvone, citronellol, 1,8-cineole, eugenol, limonene, linalool, (-)-menthol, isomenthol, (+)-menthol, menthone, β-myrcene, α-pinene, β-pinene, pulegone, terpinene and thymol were purchased from Fluka Chemicals (Germany) and Sigma (USA). The direct vapor exposure to the essential oil components on insects was tested in an enclosed chamber (70cm3) that allowed to create a vapor system. A total of 60 ml of the tested agent was used in each treatment. Control consisted of the enclosed chamber without the addition of any substance. The number of knockdown head lice was recorded at fixed time intervals of 5 min for 1h, and then a probit regression analysis was made to determine the knockdown time 50% (KT50 ) of the tested substances. The most effective vapors of the essential oil components were 1,8-cineole, anisole, limonene, β-pinene and linalool, with KT50 values of 11.1, 12.7, 27.2, 33.9 and 37.73, respectively. Regression analysis revealed a significant correlation between vapor pressures of the effective components of essential oils and KT50 estimates (P<0.05). Thus, the more volatile components  were the more effective fumigants. The findings reported herein are promising as Pediculus humanus capitis alternative control.