Interspecific hybridization of Eucalyptus as a potential tool to improve the bioactivity of essential oils against permethrin-resistant head lice from Argentina

The essential oils extracted from Eucalyptus grandis, Eucalyptus camaldulensis, Eucalyptus tereticornis, and the hybrids E. grandis × E. camaldulensis, and E. grandis × E. tereticornis were analyzed by GC–MS, and evaluated for their fumigant and repellent effects on permethrin-resistant head lice. Fumigant activity of both hybrids was higher than that for pure species. E. grandis × E. tereticornis and E. grandis × E. camaldulensis showed KT50 values of 12.99 and 13.63 min, respectively. E. grandis, E. camaldulensis, and E. tereticornis showed KT50 values of 25.57, 35.01, and 31.31, respectively. A simple regression analysis revealed a significant correlation between KT50 data and % of 1,8-cineole in these essential oils. Repellency varied from 47.80 ± 16% to 80.69 ± 6% for the five Eucalyptus essential oils tested. Interspecific hybridization improves the pediculicidal activity of Eucalyptus essential oils.