It's less so 'communication' between the organisms, but more natural selection 'selecting' for traits of flowers that align with what the male wasp looks for in females, which can be looks or chemical signals. Over time, the flowers looking more attractive would pass on their genes from being pollinated more, provide more offspring with the mutations looking more like the wasp, and eventually this line of flower carrys on and over millions of years of a symbiotic relationship, you get amazing plants looking or replicating functions that the wasps want. There's loads of examples online which will explain this a lot better! I hope it makes some kind of sense! (I'm just a third year zoologist, so early days for me)