Combined mode toxicity of different crude extracts of plants to mango mealybug Rastrococcus invadens Williams

Six acetone extracts of Annona senegalensis root-bark; Tephrosia vogelii root-bark; stem-bark, leaf and seed; Tephrosia candida seed; and two aqueous residue extracts of neem seed kernel and Annona muricata seed kernel were tested for bioactivity against Rasdtrococcus invadens Williams at different concentrations with three replications. The six acetone extracts were highly toxic to adult female R. invadens in the combined mode experiment. T. vogelii stem-bark, followed by its seed; A. senegalensis root-bark and T. candida seeds extracts, was most insecticidal to the mealybug. Respective 48-h LD50 values for T. vogelii stem-bark and seed, A. senegalensis root bark, T. vogelii leaf and T.candida seed extracxts were 4.6, 4.6, 11.1, 11.3 and 15.6 µg/insect. Generally, mortalities by each effective extract increased with increase in concentrations. Knowledge of specific mode of action of individual insecticidal extracts of plants is required for developing botanical insecticide for field control of the mealybug pest.