ABSTRACT
The silverleaf whitefly is a very important pest to tomato plants due the damages caused and its difficult control, justifying the development of alternative methods. The objective of this research was to compare the bioativity of aqueous and organic extracts (methanolic, ethanolic, chloroformic and hexanic) from T. pallida twigs and aqueous extract from neem seeds, Azadiracta indica A. Juss on nymphs of Bemisia tabaci biótype B on tomato plants. Initially, all extracts were used a at concentration of 5% to select the most efficient organic extract against the insect. The leaflets from upper part of the with 7-day old nymphs were dipped in the respective extracts for 2 sec. One week later the nymphal mortality was evaluated. The chloroformic extract was selected and compared with aqueous extracts of the two meliaceous plants in relation to the translaminar, systemic and contact actions. In the translaminar action, the extract at a concentration of 5% was sprayed on the adaxial face of the leaves of the upper part of the plant infested with 7-day old nymphs (on the abaxial face). In the systemic action, 20 mL of the extracts at a concentration of 0.5% was applied in the soil of vases of plants infested with 7-day old nymphs. In both cases the evaluation of the nymphal mortality occurred after a week of the application of the extracts. For evaluation of the contact action, 0.2 µL (0.3%) of the extracts were applied on third-instar nymphs. The nymph mortality was evaluated considering the number of empty pupal cases. In all experiments, water was used as the control. It was verified that all extracts have bioativity against the silverleaf whitefly, the aqueous extract of neem seed being the most efficient among them. In the concentrations used, the translaminar, systemic and contact actions were only observed with the aqueous extract of neem seeds.
KEY WORDS:
Azadiracta indica; Trichilia pallida; silverleaf whitefly; insecticidal plant.