On July 29, 1993, at 0720 hours Pacific daylight time, an Ayres S-2R- T34, N4016B, left main gear collapsed, which ultimately damaged the left wing spar, while taxiing for takeoff at Tulare Airport, Tulare, California. The pilot was beginning a local visual flight rules aerial application flight. The airplane, operated by Moore Aviation, Tulare, sustained substantial damage. The certificated commercial pilot, the sole occupant, was not injured. The pilot reported in a telephone interview conducted on January 13, 1994, that he had completed four aerial application flights before beginning the accident flight. Company maintenance personnel reported that the main gear strut lower inner tube assembly bolt hole cracked which ultimately led to the gear failure. The cracked hole radius displayed extensive fatigue signatures.