bacillus thuringiensis

[Fuerte Rav]

Hello all
I've found a supplier who will ship a product containing bacillus thuringiensis to me here in The Canaries.
I want to try it on my citrus trees in an effort to control Citrus Leaf Miner - the little bast*rds have decimated my trees for the last 2 years.
I've tried Neem oil and other pesticides to no avail. I've even sprayed the trees with the most obnoxious aftershave I could buy cheaply - it was meant to confuse the moths - all it did was make me stink, even after a couple of showers! I can't keep up with squashing them by hand.
So, my question is, has anyone used bacillus thuringiensis and can give me some advice?
Do I just spray once and that is it for ever? Or do I need to spray each season, or every month?

Hopefully details will be on the product when it arrives - I couldn't read the pic online - but I'd like to hear of anyone's experience of using it while I'm waiting.
Thanks