Some of us here believe that ants cause fruit set, presumably by pollinating.
To pollinate a female-stage flower by hand, one does have to force-open a wide-enough opening to stick in a finger, get some "stickum" on the finger, then stick the same finger into a container that one has gathered pollen in, then return the now-pollen-covered finger into the female stage flower. Brushes don't work well with soursops. [Bushes do work well with atemoyas, cherimoyas, sugar-apples, etc., that have three petals.] Soursop pollen is gathered fresh after sunset, and is used immediately.