Allium sativum essential oil: Different susceptibility of Diptera larvae and adults to its arsenal of sulfur derivatives

Essential oils (EOs) have varied compositions depending on several intrinsic and extrinsic factors. Despite being generally indicated as valuable insecticides, the prevalence of a chemical class can determine an EO’s more or less marked bioactivity. For this purpose, we selected an Allium sativum L. EO rich in sulfur derivatives, Cinnamomum verum J.Presl EO characterized by phenylpropanoids, Origanum vulgare L. EO chiefly composed of oxygenated monoterpenes, and Ruta graveolens L. EO abundant in non-terpene derivatives. The complete composition of the EOs was ascertained through gas chromatography-electron impact mass spectrometry. As insect pests of economic relevance, we focused on the Diptera the blue bottle fly Calliphora vomitoria (Linnaeus) (Calliphoridae) and the Mediterranean fruit fly Ceratitis capitata (Wiedemann) (Tephritidae). The mean lethal concentrations (LC50) by fumigation and mean lethal doses (LD50) by direct contact of the four EOs on adult specimens and wandering larvae were evaluated. The A. sativum EO was identified as the only one able to control both developmental stages of the target pests. Besides highlighting a different susceptibility between the two flies, with Ca. vomitoria being less susceptible (susceptibility ratios – SR from 1.37 to 26.29), we also observed a distinctly lower susceptibility of the wandering larvae compared to their respective adults (SR with the A. sativum EO of 15.64 by fumigation and 156.17 by contact for Ca. vomitoria; 72.42 and 107.29, respectively for Ce. capitata). Therefore, species-specific susceptibility of insects, regardless of body size but related to ontogeny and different levels of detoxifying enzymes possessed, can be hypothesized.