Toxic effect of aliphatic alcohols against susceptible and permethrin-resistant Pediculus humanus capitis (Anoplura: Pediculidae)

The effectiveness of I-octanol, 1-nonanol, 1-decanol, 1-undecanol, and I-dodecanol was evaluated by immersion method against susceptible and permethrin-resistant head lice, Pediculus humanus capitis De Geer, from Buenos Aires, Argentina. All the tested alcohols showed knockdown effect at 10 min and mortality 18 h after treatment. The highest activity was found for the I-dodecanol (KC50 2.55%, LC50 2.28%) and the lowest for 1-octanol (KC50 8%, LC50 4.46%). The toxicity to the head lice systematically increased with the increase in carbon atoms in the n-aliphatic alcohol moiety, and with the octanol:water coefficient (r(2) = 0.94). The pediculicidal activity of I-dodecanol was not correlated with resistance to permethrin, because no significant difference was observed between toxicity parameters in the susceptible (MAR) and the permethrin-resistant populations which bad different resistant levels (RR 5.77 x for E49 population, RR 9.5 x for HL population and RR > 35.3 x for GH population). The pediculicidal effect of aliphatic alcohols demonstrated in this study and the lack of correlation with the permethrin resistance may prove to have a practical value for use in susceptible and permethrin-resistant head lice control.