Is it legal for a wrestler to tickle his opponent?
 

Is it legal for a wrestler to tickle his opponent to gain an advantage?

Probably not illegal.
If it was illegal, an opponent in a near pin position could just start laughing and say that he is being tickled. ;)

My thought is that it is nearly impossible to tickle someone that is actively wrestling against another wrestler. The spasms that tickling cause are not likely to happen when an athlete is actually wrestling. Now, having said that, if a wrestler was trying to do something like that during a match my inclination would be to penalize them for unsportsmanlike conduct. Any maneuver that is designed to punish rather than complete the goal of pinning a wrestler is illegal. Pretty hard to make the argument that "I'm trying to tickle him to his back"

I don't see the tickling as a way to punish. Is there a provision in the rulebook that gives the official the authority to prohibit something that is not a "wrestling move"?

As I said, any maneuver that is not specifically designed to control or turn an opponent would likely be unsportsmanlike or taunting and I would penalize it.

It doesn't have to be tickling, you could be mussing up his hair or whispering to him or winking or any number of other stupid things but it is not wrestling and has no place on a mat.