Responses of the sweetpotato whitefly, Bemisia tabaci, to the chinaberry tree (Melia azedarach L.) and its extracts

Host preference bioassays for adults of the sweetpotato whitefly were perfo rmed with leaves of the chinaberry tree Melia azedarach L., tomato, cucumbe r and bean. Fruit and leaf extracts: of the chinaberry tree were tested aga inst adults of the sweetpotato whitefly. Fruit extracts were tested against eggs, first and second instar nymphs, and pupae of the insect. Treatments included aqueous, methanol, and acetone fruit extracts of 200 mg ml(-1) and serial dilutions of 20.0 and 2.00 mg ml(-1), ether extract, the botanical insecticides Azatin(R) and Margosan(R)-O and the control, water or water wi th Triton(R). Mortality data was collected at 6, 7, and 8 days after treatm ent of the eggs, nymphs and pupae, respectively. Results of the host prefer ence bioassays indicated a significantly lower number of live insects on le aves of the chinaberry tree vs leaves of bean, cucumber, and tomato after 2 4 h. This indicates that M. azedarach is not a good host for the sweetpotat o whitefly. Adults of the insect were significantly more repelled from toma to plants treated with the undiluted extracts when compared to the control after 72 h. There were significant differences in percent mortality of nymp hal instars when exposed to the undiluted extracts compared to other extrac ts and the control. However, there was no significant effect of the fruit e xtracts on the egg and pupa instars. Thus M. azedarach extracts were found to be repellent to the whitefly adults, while the fruit extracts have shown a significant detrimental effect against early nymphal instars. In general , the methanol extracts were more active against B. tabaci than extracts wi th other solvents.