HORTICULTURAL ENTOMOLOGY Fumigant Toxicity of Summer Savory and Lemon Balm Oil Constituents and Efficacy of Spray Formulations Containing the Oils to B- and Neonicotinoid-Resistant Q-Biotypes of Bemisia tabaci (Homoptera: Aleyrodidae)

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 identiÞed compounds of the oils, as well as of the control efÞcacy of four experimental spray formulations containing individual oils (0.5 and 0.1% sprays) and spinosad 10% suspension concentrate (SC) to females from Band neonicotinoid-resistant Q-biotypes ofBemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). Based on 24-h LC50 values, Q-biotype females (0.20 g/cm ) were 40 times less susceptible to dichlorvos than B-biotype females (0.005 g/cm). Thymol (LC50, 0.35 g/cm ) and carvacrol (0.56 g/cm) were the most toxic compounds toward Q-biotype females, followed by (1S)-( )-borneol, -terpineol, nerol, linalool, and carvone (1.06Ð1.38 g/cm). 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 commonmode of action or elicit cross-resistance. The 0.5% sprayofLBO, SSO, and spinosad 10%SCresulted in 90%mortality towardbothbiotype females. Global efforts to reduce the level of toxic synthetic insecticides in the agricultural environment justify further studies on LBOand SSO-derived materials as potential contact-action fumigants for the control of B. tabaci populations.