Physiochemical parameters related with the bioactivity among essential oil components against permethrin-resistant Pediculus humanus capitis (Anoplura: Pediculidae).

ARIEL C. TOLOZA1, GASTÓN MOUGABURE-CUETO1, J. ZYGADLO2, EDUARDO N. ZERBA1 & MARIA I. PICOLLO1

Buenos Aires

Congreso; International Congress on Phthiraptera; 2006

CIPEIN

Resistance to permethrin and other pyrethroids in Pediculus humanus capitis from Buenos Aires, Argentina, was previously reported by our laboratory in 1997. The use of essential oils for the control of resistant head lice is an interesting alternative to permethrin because they are environmental friendly and not acutely toxic to mammals. Previous studies in our laboratory have shown the fumigant and repellent activity of native and exotic essential oils and their components. The purpose of the present study was to determine physiochemical parameters related with pediculicidal activity relationships among the effective essential oil components. Head lice were collected from heads of infested children 5-12 yr old, using an antilouse comb. Once the fumigant (knockdown time 50% KT50s) and repellent (Repellency indexes RI) data were collected, a multiple linear regression analysis was performed to examine relations among KT50s, RIs and either their respective vapor pressures or octanol-water partition coefficient values (log P). Fumigant regression analysis revealed a significant correlation between KT50 and corresponding vapor pressures of the effective components of essential oils when considered as a single predictor (r2=0.42, F=5.74, P<0.05). Thus, the more volatile the compound, the more effective it was as a fumigant. In contrast, KT50s were independent of log P values for the same compounds (r2=0.001, F=0.01, P<0.937). When both predictors were included, the resulting model showed a better correlation (r2=0.73, F=8.14, P<0.05). Concerning repellency regression analysis, either the regressions between RIs and vapor pressures or RIs and log P showed r2=0.001 and P>0.05. Most of the components that were effective in vapor phase were not the same that were effective as repellents in contact exposure. Our results provide indications of a possible difference between the knockdown and repellency targets of essential oils components