An assessment was made of the fumigant toxicity of 36 constituents from lemon balm oil (LBO) and summer savory oil (SSO) and another additional nine previously identified compounds of the oils, as well as of the control efficacy of four experimental spray formulations containing individual oils (0.5 and 0.1% sprays) and spinosad 10% suspension concentrate (SC) to females from B- and neonicotinoid-resistant Q-biotypes of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). Based on 24-h LC₅₀ values, Q-biotype females (0.20 µg/cm³) were 40 times less susceptible to dichlorvos than B-biotype females (0.005 µg/cm³). Thymol (LC₅₀, 0.35 µg/cm³) and carvacrol (0.56 µg/cm³) were the most toxic compounds toward Q-biotype females, followed by (1S)-( — )-borneol, α-terpineol, nerol, linalool, and carvone (1.06–1.38 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 LBO, SSO, and spinosad 10% SC resulted in >90% mortality toward both biotype females. Global efforts to reduce the level of toxic synthetic insecticides in the agricultural environment justify further studies on LBO- and SSO-derived materials as potential contact-action fumigants for the control of B. tabaci populations.