Bioactivity of formulas containing essential oils from the family Myrtaceae for the management of deltamethrin-resistant Plutella xylostella (L.) (Lepidoptera: Plutellidae)

Plutella xylostella is the major pest of Brassica and is resistant to more than 95 synthetic insecticides, including deltamethrin, which is frequently used in family farming activities in the state of Pernambuco, Brazil. A possible strategy for overcoming such resistance is the use of botanical insecticides containing essential oils. The aim of the present study was to determine the chemical composition of essential oils from Syzygium aromaticum, Melaleuca alternifolia, Melaleuca leucadendra, Eucalyptus citriodora and Eucalyptus globulus and evaluate the effects of these oils as well as selected constituents (beta-pinene, alpha-terpinene, rho-cymene, limonene, 1,8-cineole, gamma-terpinolene, citronellal, terpinen-4-ol, eugenol, beta-caryophyllene and E-nerolidol) on different stages of development of two populations of P. xylostella - one susceptible and one resistant to deltamethrin. Chemical analysis by gas chromatography-mass spectrometry revealed eugenol (S. aromaticum), 1,8-cineole (E. globulus), citronellal (E. citriodora), terpinen-4-ol (M. alternifolia) and E-nerolidol (M. leucadendra) to be the major constituents. Among the oils tested, S. aromaticum was the most promising in the different modes of action and had the same level of toxicity to the two populations of P. xylostella analyzed. Among the constituents, E-nerolidol and terpinen-4-ol exhibited promising larvicidal action, whereas limonene exhibited promising ovicidal and antifeedant action. None of the oils presented severe phytotoxicity to the host plant. All results were compared to those achieved with deltamethrin and azadirachtin, which were used as positive controls. The deltamethrin-resistant population of P. xylostella did not exhibit pre-adaptive resistance to the oil from S. aromaticum or E-nerolidol, terpinen-4-ol and limonene.