The insects look like aphids. I've never seen aphids kill flower buds, so I wonder if they are the direct cause? And the rose appears to be what is known in the US as "Banshee," apparently the same as the rose grown in Sweden as 'Minette' or Rosa suionum. And if that's the case, their buds will "ball" in damp weather, rotting away as you describe, independent of the aphids. The new book-form special issue of Rosa Mundi (journal of the Heritage Rose Foundation and available through their website) has an article on "Banshee," as well as one on old roses in Sweden which discusses this rose there.

Maybe even a 'bad' picture would help. There are lots of possibilities that fit this description.

Found a couple ===>>> in a former life.. i was a lawn warrior ... grubs could destroy large swaths of lawn ... WHEN THE POPULATION GOT OUT OF CONTROL ... you would go rake out and a square foot of the dead lawn .. and you would count how many you found.. though by this time.. you knew there were lots of them ... anyway.. you would find a dozen or two per square foot ... that is why the lawn died.. i mean really.. grass is the most invasive weed on the face of the earth ... growing anywhere .. lol ... at that point.. there were .. and i presume still are ... lawn chems that you could apply to your lawn to fix that problem ... if you find a couple.. in an entire garden bed.. it really is... ugly and ikky as they are ... NOT A PROBLEM that need be fixed .... IPM .. integrated pest management requires that there be a problem .. that needs to be fixed.. before you go all nuclear war on getting rid of every bug in your yard ... i suggest you try to accept mother natures wonder.. and just enjoy the process ... which includes ikky bugs ... and move on ... i also used to carry them to the cement ... and just leave them there for the birds .... even if they didnt find them the sun would kill them .. its not like they have legs to go anywhere else ... lol ... but i dont ever recall them being there a few minutes later ... ken

Other than the arborvitaes (and their leafminer IS a moth). Most leafiners are more of a cosmetic issue than something that actually harms plants. I never bother to treat for them. And beneficial wasps parasitize a lot more problem pests than just leafminer larvae. I would encourage them before I'd try to eliminate something else that is really not much of a problem at all.