Hi Mary,

I'm sorry to hear about your flowers!  When I first looked at your photos I thought you had tobacco budworms, a type of caterpillar, but on closer inspection it looks actually like those are the ripe fruits of petunias releasing their seeds.  

By removing those fruits, ideally when they're still developing right after petals drop from them, you can prolong the flowering of annuals like petunias.  Once they have set some seed to ensure the next generation, many varieties significantly slow flowering.  Hot weather doesn't help, either.

I think carefully removing any spent flowers that you can find and giving the plant a dose of fertilizer (if you haven't been fertilizing regularly) will give you a late summer bloom-boost.

I hope this is helpful.

Cordially,

John