Eucalyptus essential oil toxicity against permethrin-resistant Pediculus humanus capitis (Phthiraptera: Pediculidae)

During the past decades, chemical control against the head louse Pediculus humanus capitis De Geer has been based in the application of products containing permethrin. The repetitive overuse of pediculicides has resulted in the development of high levels of resistance to one or more of these products worldwide. Essential oils obtained from aromatic plants like Eucalyptus are good and safe alternatives due to their low toxicity to mammals and easy biodegradability. In the present study, we reported the chemical composition of Eucalyptus dunnii and Eucalyptus gunni, and the fumigant activity of five Eucalyptus essential oils and their main compounds against permethrin-resistant head lice from Argentina. The most effective essential oils were Eucalyptus sideroxylon, Eucalyptus globulus ssp globulus, and Eucalyptus globulus ssp maidenii, with knockdown time 50% (KT₅₀) values of 24.75, 27.73, and 31.39 min. A linear regression analysis between percentage of 1,8-Cineole and KT₅₀ values of the essential oils showed a significant correlation at a p < 0.01. Since Eucalyptus essential oils showed to be effective against head lice and are classified as safer compounds, they can be employed into pediculicide formulations.