Which sentence needs a hyphen?

A. the television station was broadcasting live.

B. crickets are most active after dark.

C. She is a self proclaimed expert on insect behavior.

D. he wants to join the high school swim team.

The sentence that needs a hyphen is C. She is a self proclaimed expert on insect behavior.

You absolutely have to have a hyphen between the words self and proclaimed (self-proclaimed) because it is a compound adjective (meaning that it consists of more than one word) which is why it has to be hyphenated. The remaining options are okay they way they are written.