Hi,

Look here for a good description of what is causing the Vapor/wing vortices: http://en.wikipedia.org/wiki/Wingtip_vortices

The reason you see it a lot when a fighter is pulling G's is because the pressure differential between the top and bottom of the wing is a lot higher compared to just flying straight and level at 1 G. At 9 G's the wing is producing 9 times the lift. Also the Angle of Attack AOA on the wing is higher during these maneuvers and causes eairlier seperation of air flow over the wings surface and also increases induced drag: http://en.wikipedia.org/wiki/Induced_drag

RUN