I use nictone (its like VX nerve gas for insects) - soak three or four cigarettes in 1 litre of water for 24 hours, boil it for a minute or two (in case the tobacco plant had some disease), then spray your plant every two days for a week or so, depending of the life cycle of the pest.

I just cleared up a nasty thrip case using this. It's 100% natural, and the nictone breaks down after a couple of weeks.