Essential oils (EO) are a great antimicrobial resource against bacterial resistance in public health. Math models are useful in describing the growth, survival, and inactivation of microorganisms against antimicrobials. We evaluated the antimicrobial activity of Melaleuca armillaris EO obtained from plants placed in the province of Buenos Aires (Argentina) against Staphylococcus aureus. The minimum inhibitory and bactericidal concentrations were close and decreased, slightly acidifying the medium from pH 7.4 to 6.5 and 5.0. This result was also evidenced by applying a sigmoid model, where the time and EO concentration necessaries to achieve 50% of the maximum effect decreased when the medium was acidified. Moreover, at pH 7.4, applying the Gompertz model, we found that subinhibitory concentrations of EO decreased the growth rate and the maximum population density and increased the latency period concerning the control. Additionally, we established physicochemical parameters for quality control and standardization of M. armillaris EO. Mathematical modeling allowed us to estimate key parameters in the behavior of S. aureus and Melaleuca armillaris EO at different pH. This is interesting in situations where the pH changes are relevant, such as the control of intracellular infections in public health or the development of preservatives for the food industry.

The insecticidal activities of essential oils (EO), the remaining water phase (RW) from the hydrodistillation, and the dichloromethane and methanolic extracts from Gutierrezia repens Griseb. and Gutierrezia mandonii (Sch. Bip.) Solbrig were evaluated. The GC and GC/MS analyses of the oils resulted in the identification of 52 compounds from G. mandonii and 17 compounds from G. repens comprising 88.7% and 98.5% of the oils, respectively. Sabi- nene (0–13.1%), β-pinene (6.4–17.8%) limonene (0.7–13.3%), (E)-β-ocimene (1.3–7.0%), terpinen-4-ol (0.7–4.1%), spathulenol (0–4.1%) and, the isomers (6R,7R)-bisabolone (6.6–58.0%) and (6S,7R)-bisabolone (0–1.6%) were the main components of the oils. Mortality and development delays of Ceratitis capitata larvae, reared using a treated artificial diet, were recorded. Gutierrezia mandonii methanolic extracts and the oil produced lethal effects (p≤0.05). Methanolic and dichloromethane extracts, the oil and the remaining water from distillation (RW) produced sublethal effects. Meanwhile dichloromethane and methanolic extracts, the oil and RW from G. repens resulted in significant mortality (p≤0.05), and all causing also significant development delays. The required concentration of G. repens oil to avoid development in 50% of C. capitata larvae (EC₅₀) was significantly lower than G. mandonii

The essential oil of the aerial parts of Cunila spicata Benth. (Lamiacaeae), was obtained by hydrodistillation and investigated by capillary GC and GC/MS. Fifty one components representing 91.8% of the oil were identified, consisting mainly of monoterpene hydrocarbons and oxygenated derivatives. The major constituents were limonene (25.9%), geranyl acetate (21.8%) and linalool (21.2%).