ABSTRACT

The effect of organic extracts from Azadirachta indica. Melia azedarach. Toona ciliata and Trichilia pallida (Rutales: Meliaceae) on eggs and nymphs of Bemisia tabaci (Hemiptera: Aleyrodidae) B biotype was assessed. Leaves and branches were dried, ground and submitted to extraction (Soxhlet) with dichloromethane and ethanol. To establish an adequate concentration for the subsequent tests, eggs were used originating from 40 adults maintained for 24h on tomato leaves in voile cages. After 9 days, the number of nymphs was determined and the dichloromethane extract from T. pallida leaves was sprayed at different concentrations (0.32, 0.56, 1.0, 1.8 and 3.2%); water and acetone were also used (controls). The nymphal mortality was evaluated after 7 days. An entirely randomized design was used, with 7 treatments and 4 replications. Afterwards, dichloromethane and ethanol extracts were sprayed on eggs at the selected concentration (0.56%), in different experiments. After 9 days, the egg mortality was evaluated and a new spraying was conducted to assess the nymphal mortality after 7 days. These experiments were conducted in a randomized block designed (10 treatments and 4 replications). The data was submitted to regression analysis, analysis of variance and compared by the Tukey test. A higher yield was observed for the ethanol extracts in relation to the dichloromethane extracts. The dichloromethane extracts from leaves and branches from meliaceas significantly affected the survival of the whitefly eggs and nymphs. The ethanol extracts affected the nymphal phase, but did not present ovicidal activity.

KEY WORDS
Insecta; whitefly; allelochemicals; limonoids