Chemical identification and insecticidal effect of Tephrosia vogelii essential oil against Cerosipha forbesi in strawberry crop

Abstract Botanical insecticides based on oils and plant extracts have proven to be an efficient alternative method for pest control, as required by agroecological systems. Tephrosia vogelii (Hook.f.) has been used in agriculture as a source of green manure and in the control of pests and diseases. However, there are few studies regarding the use of compounds derived from the secondary metabolism of this plant. Chemical compounds present in the essential oil of Tephrosia vogelii flowers were identified, aiming at its use to control the aphid Cerosipha forbesi in the strawberry crop. Bioassays were carried out under laboratory and semi-field conditions, with different concentrations of the essential oil and the lethal concentrations LC50 and LC90 were estimated. Only two groups of terpenic compounds were identified in the essential oil of T. vogelii: monoterpenic hydrocarbons (alpha-pinene; limonene and ocimene) and oxygenated sesquiterpenes (nerolidol, spathulenol and farnesol). The essential oil of T. vogelii presented toxic effect against C. forbesi, with the LC50 and LC90 of the insect population estimated at 0.106 and 0.380 mL/L, respectively. Under semi-field conditions, mortality increased at higher concentrations, and the LC50 and LC90 were estimated at 0.114 mL/L and 0.465 mL/L, respectively. Mortality over 90% was observed after 24 h of the essential oil application, for all of the tested concentrations, showing an insecticidal action of the oil against the aphid C. forbesi.