Aphids are attracted to the tender new growth. Here is a time-lapse of rose leaf bud growing and as it does becomes infested with aphids.
At the end of the sequence, one of the natural aphid preditors the hoverfly larva comes in and eats most if not all of the aphids.
This shows just how efficient hoverfly larvae are at controlling aphids.
The sequence was filmed over a period of 24 hrs.