Green fly in my greenhouse already!

I've had greenfly thick on my climbing roses since the start of April, and I mean so thick that some of the stems looked double their actual thickness. But I gritted my teeth and ignored them - there were too many to deal with anyway except with chemicals, which I won't do. Finally I'm starting to see ladybirds appearing, in fact I saw a pair mating yesterday, so I know help will soon be on hand, and in a couple of weeks the greenfly will be gone.