The airplane was destroyed when it impacted trees and terrain following a loss of control during flight. The pilot reported that he had performed a pre-flight examination of the airplane and no discrepancies were found. He said that after takeoff, he noticed that the airplane was flying left wing heavy. He said that he climbed to pattern altitude where he attempted a turn to the right. The right turn required more aileron input than was normal and the pilot decided to return to the airport. He said that he then made a left turn which became steep and he attempted to level the wings using right aileron at which time he felt something "let go." He was no longer able to control the airplane and it subsequently impacted trees and terrain. Examination of the airplane after the accident revealed that the left aileron push-pull control rod was separated into two pieces. Examination of the separated end fitting had portions of two rivets at 90 degrees to each other within the shank portion that inserts into the aluminum tube. The rivet shanks appeared to be machined or filed flush with the outside diameter of the insert. The aluminum pushrod tube had no evidence of drilled holes corresponding to the end fittings rivet locations, and no manufactured or shop formed rivet heads were present. No evidence could be found to indicate that the retaining rivets had been installed in the aluminum tube.