Insecticidal toxicity of Eucalyptus cinerea essential oil and 1,8-cineole against Musca domestica and possible uses according to the metabolic response of flies

• Eucalyptus essential oil an effective fumigant against Musca domestica adults.
• Flies metabolized 1,8-cineole to 2,3-dehydro-1,8-cineole and α-terpineol.
• A P450 inhibitor, increases the toxicity of the essential oil and 1,8-cineole.
• 1,8-Cineole acts as P450 inhibitor-like compound increasing toxicity of deltamethrin.

In a fumigant assay, Musca domestica adults treated with Eucalyptus cinerea EO [LC50 = 5.5 mg/dm3; majority component by SPME–GC: 1,8-cineole (88.5%), α-pinene (2%), α-terpineol (9%)], died within 15 min or less. The terpenes absorbed by the flies and their metabolites, analyzed using SPME fiber, were 1,8-cineole (LC50 = 3.3 mg/dm3), α-pinene (LC50 = 11.5 mg/dm3), α-terpineol (LC50 = 36.8 mg/dm3) and a new component 2,3-dehydro-1,8-cineole, in proportions of 74%, 0.1%, 24.7% and 1.2% respectively. 2,3-Dehydro-1,8-cineole and α-terpineol were formed by oxidation of 1,8-cineole mediated by cytochrome P450, as demonstrated by a fumigation assay on flies previously treated with piperonyl butoxide, a P450 inhibitor, which showed an increase in toxicity of the EO and 1,8-cineole, supporting its participation in the formation of metabolites. We also demonstrated that 1,8-cineole acts as a P450 inhibitor-like compound, improving the toxicity of other xenobiotics such as deltamethrin.

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