what kind ants you got Durian Lover? Any chance Red Tree ants, the leaf cutter ant? Why would they aid pollination?
I chased mine out of the tree, they went crazy over the fruit, kept trying to build nests around the soursop fruit, laying eggs right on the node, they had about 4 other nests in the tree at the same time, I chase them out of every tree they come into by hosing them down everyday.
My first fruit was a bit elongated, size of a small Durian, not as big as some seen, but definitely twice the size of a softball, sweet, less acid then the ones I ate in Hawaii before.