Preparation and characterization of Mentha × piperita oil emulsion for housefly (Musca domestica L.) control

Emulsified concentrate (EC) formulation of Mentha × piperita oil was prepared by taking (w/w) 40% oil, 45% aeromax, 3% butanol-1 and 12% surfactant (CABS-70 and NP-20 in variable ratio). Three ECs (designated as A, B and C) were screened amongst prepared ECs on the basis of physical criteria. Emulsions were assessed for their stability through creaming volume, particle size and zeta potential determination. Particle size of emulsions varied between 536.7 and 1133.6 nm, while zeta potential value (−45.9 to −47.3 mV) was strongly negative suggesting stability. Characterization of emulsion for its pH (≈6.6–7.5) and flash point analysis (≈90–92 °C) indicated a stable formulation, which was safe to handle and transport. Prepared emulsions were stable at various temperatures (4–60 °C), and showed a thin creaming layer at the upper surface without any phase separation, when subjected to centrifugation. Freeze/thaw cycles showed no visible change in appearance in EC ‘A’ and ‘B’, while EC ‘C’ showed tendency to rupture, i.e. dispersion of oil droplets in emulsion, after 6 cycles. Bioefficacy of EC ‘B’, adjudged as most stable emulsion, against adults of housefly (Musca domestica) showed 70–88% repellency with freshly prepared EC. The repellency decreased to 34–72% after 12 months storage at room temperature. Assay against housefly larvae showed an LC50 value of 0.08 μL/cm2 (emulsion from freshly prepared EC) and 0.34 μL/cm2 (emulsion from stored EC).

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► Preparation and characterization of Mentha piperita oil emulsion.
► Effect of process parameters on emulsion resolved.
► Insecticidal activity determination of Mentha piperita oil emulsion against housefly.
► Shelf life of emulsion analyzed in terms of its bioactivity.