An assessment was made of the fumigant toxicity of 20 constituents from catnip oil and another additional five previously identified compounds of the oils and control efficacy of three experimental spray formulations containing catnip oil (1, 0.5 and 0.1% sprays) to females from B- and neonicotinoid-resistant Q-biotypes of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). Spathulenol (LC50, 0.39 μg/cm3) and thymol (0.45 μg/cm3) were the most toxic compounds, followed by carvacrol, α-terpineol, nerol, linalool, menthol and eugenol toward Q-biotype females (0.85–1.24 μg/cm3). The toxicity of these compounds was virtually identical toward both biotype females, indicating that the terpenoids and the insecticides (neonicotinoids and dichlorvos) do not share a common mode of action or elicit cross-resistance. The 0.5% spray of oil formulation resulted in > 80% mortality toward both biotype females. Global efforts to reduce the level of toxic synthetic insecticides in the agricultural environment justify further studies on catnip oil-derived materials as potential contact-action fumigants for the control of B. tabaci populations.