Tim C. writes
Following up to "Martin Brown" :

It used to be used as an insecticide in the old days..

and still is, from the point of view of the tobacco plant itself. ;-)

This has always puzzled me. I assume most of Nicotiana contain nicotine?
- or is it just the tobacco plant itself? Nicotiana sylvestris, for
example, is a magnet for whitefly. Its main defence seems to be the
stickiness of its leaves, but it doesn't protect very well - the heavy
infestation that it attracts causes real damage.
--
Kay