Determination of the biocidal activity of plant extracts against the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae)

The whitefly Bemisia tabaci Genn. is a pest. It causes economic losses in crop production and it is distributed worldwide. The combat against it is usually based on repetitive applications of chemical pesticides, resulting in environmental contamination and genetic resistance of insect populations. This research was carried out with the objective of evaluating the insecticidal activity of nine plant extracts in adults of B. tabaci, under in vitro experimental conditions. Toxicity bioassays with the ethanolic extracts of each plant at a concentration of 5000 mg/L were tested to determine the one with the best performance. The plant species used were Enterolobium cyclocarpum (leaves and bark), Lippia graveolens (leaves), Ruta graveolens (leaves), Adonidia merrillii (leaves and fruits), Annona muricata (seeds), Curcuma longa (root) and Zingiber officinale (root). The most toxic extract was R. graveolens; it was fractionated by column chromatography with three solvents of increasing polarity: isopropanol: dichloromethane (8:2), ethanol 96% and water. Finally, bioassays were carried out with the three phytochemical partitions to determine their activity and to approximate to the type of compounds responsible for the toxic activity. The least polar fraction (isopropanol: dichloromethane [8:2]) was the one that caused the highest mortality. The research sought to provide a basis for the creation of alternative control methods against the pest in study, under the assumption that plant extracts are a promising option for the development of bio-insecticides safer for the environment and human health.