The pilot was on the last local aerial application flight of the day. Prior to starting the job, he flew above and around the field to check for obstructions and power lines. The field had numerous electrical feeder wires running throughout the job site, with north-south power lines on the west and east ends of the 1/2-mile-long field. This application required the material to be applied while making east-west passes above the feeder wires and oil pumps. Upon maneuvering onto the last eastbound pass, he applied aft cyclic to climb above the location of feeder wires. Several seconds later, he felt a sudden jarring and vibration emitting from the rear portion of the helicopter. He felt that he had possibly struck a wire that he did not see, and continued flying the helicopter in an eastbound direction to perform an emergency landing. As he began slowing, the front of the helicopter began yawing to the right in a southeast direction. It was headed towards a triple strand of east-west power lines and a small oil pump positioned approximately 25 feet south of the triple strand electrical lines. In anticipation of a second wire strike, he closed the throttle and began an autorotation prior to the helicopter striking the east-west power lines. It came to rest in an upright position facing in a southwest direction. He could hear the engine operating and performed emergency engine shutdown procedures. He exited the helicopter after all motion stopped, and met his field supervisor, who had already arrived and disconnected the aircraft battery. The tail rotor made contact with the first set of power lines and separated along with its gearbox. The helicopter sustained substantial damage to the main rotor blades and fuselage after the second contact.