Joanne,

Since my house is full of nicotiana (I only found it for sale once at K-mart, a marked down part empty flat), I was searching to see how many I might need. Anyway, I ran onto this page that says you can use the ornamental plants just as you wish to use tobacco for insecticide.

http://www.tulipsinthewoods.com/flowering-plants/nicotiana-alata/

I still don't know if 6 will be enough though or if I need all 8 big ones. I didn't have great germination on the alata but the seed was old.

Diana