That's a good question. It's a difficult one to respond to, but I'll try to do the best I can. I've had a career long enough now that I can actually remember different waves of gypsy moth. I've worked mostly in eastern Canada, although I did work two summers on Vancouver Island, at MacMillan Bloedel and Weldwood, actually, as a student. It seems that left to its own devices, the European gypsy moth has been mostly controlled, if you will, by natural predators. It's actually quite an amazing story.
I was a forester at one point. Before Tree Canada, I worked for the Ontario Ministry of Natural Resources, and I remember in the early nineties when I had to respond to a gypsy moth infestation north of Toronto in a township called the Township of King. I remember that the ministry was proposing a spray with Bt, which is a natural bacteria that the insect ingests. It kills the insect and has no effect on other wildlife, so it's very good to use. It was in a forest situation. I remember the mayor calling me, very upset with respect to the spraying, but years later, when the infestation arrived at her doorstep, she was on the phone again asking, “Where's the ministry?” and that sort of thing.
On a single tree, I think it's very difficult to use those products. In a forest situation, they can be used and Bt seems to be the one to go with.