I presume you mean blackfly? I'm not aware of ones with orange spots, but ladybird larvae are black with orange spots and they eat loads of blackfly. have you got a picture of these creatures?

If the 'blackfly' are not winged, then they're probably ladybird larvae, as Pam says above. Blackfly are very small, completely black flies with wings.

I have never seen Blackfly on my Choisya,Sylvia..so the above comments are more likely..

Small and narrow, black with orange/red marks and wandering around on their own sounds like ladybird larvae to me. Blackfly come in masses, don't have any marks (so far as I've seen) are usually on the tips of the leaves. If they are ladybird larvae then please leave them be as Pam24 says they eat lots of greenfly etc.

Blackfly would be eliminated around now, as it is time to clip back Choisyas if they need a clip. I just have one more to do when I have room in my green bin. These ladybird larvae will soon turn into ladybirds and look pretty on your leaves and do some good too.

Thank you for your replies, I quess it must be the ladybird larvae that is the ones with the orange markings, but if so they are not able to get rid of all the masses of blackfly that are on the plant. The plant suddenly shoots up large stalks and they are all covered with this smaller blackfly. So there are two types of bug on it. I am still not sure what to do,but have cut the top worst bits off. Should I cut it right down to the ground? I have another variety of Choisya on other side of garden and that is not affected although has not many flowers this year.

You could trim it down pretty generously but surely not to the ground Sylvia. Blackfly usually gather on the new growths that spurt after flowering and they are the ones that need to be taken back. You can be very savage with Choisya if you want to, and in time it will grow back. The bare space may not look good. I know if I trim my remaining one back too much I will have a comment from my neighbour. We are very friendly.... but he will say 'why cut so much off?' I will say I can't let it get too large, as Choisya does if you allow it to keep growing.