To obtain the oregano dose response curve, oregano essential oil concentrations of 1.25, 2.5, 5 and 10% (w/v) were prepared using reagent alcohol as a vehicle. Based on the results of this study, the dose of 2.5% was chosen for the following experiment as it was the minimum dose at which repellent effect was observed until 24 h. For the next experiment, the repellency of catnip and oregano essential oils, their mixtures and carvacrol were tested at a final concentration of 2.5% (w/v). Previously, the dose of 2.5% of catnip essential oil has also shown excellent repellency up to 24 h in bed bugs (data not shown). The mixtures were included to determine the combined repellent effect of two essential oils that have shown strong repellency against bed bugs previously. Carvacrol, the major constituent of oregano essential oil was also evaluated to determine the repellent effect of the oregano essential oil as whole along with its major compound. The 2.5% (w/v) of catnip and oregano essential oil solutions along with carvacrol (Sigma Aldrich, St. Louis, MO) were prepared in reagent alcohol.
The mixtures of N. cataria cv. CR9 (NC) and O. vulgare cv. Pierre (OV) essential oils in three different ratios of 25:75 NC : OV, 50:50 NC : OV, 75:25 NC : OV were prepared using reagent alcohol as a vehicle. Mixtures of catnip and oregano essential oil as active ingredients in ratio of 25:75 NC : OV were prepared with 0.625% (w/v) of catnip and 1.875% (w/v) of oregano, mixture with equal parts (50:50 NC : OV) was prepared with 1.25% (w/v) of each essential oil and finally, the mixture of 75:25 NC : OV was prepared with 1.875% of catnip essential oil and 0.625% of oregano essential oil. Concentration-based repellent effects of catnip cv. CR9 have already been established (Reichert et al., 2019 (link); Shi et al., 2021 (link)) and as such a dose response curve of catnip essential oil was not evaluated in this study. A 2.5% solution of DEET (N,N-diethyl-meta-toluamide) (Sigma Aldrich, St. Louis, MO), the positive control was also prepared using reagent alcohol which was used as negative control. The solutions were stored in clear, 30 mL plastic spray bottles.
The mixtures of N. cataria cv. CR9 (NC) and O. vulgare cv. Pierre (OV) essential oils in three different ratios of 25:75 NC : OV, 50:50 NC : OV, 75:25 NC : OV were prepared using reagent alcohol as a vehicle. Mixtures of catnip and oregano essential oil as active ingredients in ratio of 25:75 NC : OV were prepared with 0.625% (w/v) of catnip and 1.875% (w/v) of oregano, mixture with equal parts (50:50 NC : OV) was prepared with 1.25% (w/v) of each essential oil and finally, the mixture of 75:25 NC : OV was prepared with 1.875% of catnip essential oil and 0.625% of oregano essential oil. Concentration-based repellent effects of catnip cv. CR9 have already been established (Reichert et al., 2019 (link); Shi et al., 2021 (link)) and as such a dose response curve of catnip essential oil was not evaluated in this study. A 2.5% solution of DEET (N,N-diethyl-meta-toluamide) (Sigma Aldrich, St. Louis, MO), the positive control was also prepared using reagent alcohol which was used as negative control. The solutions were stored in clear, 30 mL plastic spray bottles.
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