ladybug larvae are blackish and leggy...don't look a thing like ladybugs...but they are beneficial, eating tons of aphids, and as far as I know, don't eat plants.
Ants on plants can be harvesting aphids (which suck the juices from plants, but don't actually "eat" them), which would explain why the ladybug larvae would be there and it could be some other pest eating your plants.
Can you get a photo of the bug? How large is it?

Kristine - You're looking at the nasty larval stage of a keelbacked treehoppers (Antianthe expansa), one pest that seems to really love night blooming jasmine (Cestrum nocturnum), also known as night blooming jessamine. This plant is a member of the Tomato or Nightshade Family (Solanaceae), as are brugmansias, daturas, tomatoes, white potatoes, green and red peppers, petunias, and tobacco. When the larvae develope they'll turn into green triangular insects. I used to get them all the time on many plants in the Solanaceae family. The article below has a photo and some info on them.

Because I don't like to use pesticides I found that the best removal techniques involved spraying them with water and hand-squishing wearing vinyl gloves. Also, look for little yellow eggs (I think they're on the underside of the leaf) and dispose of them. Be diligent and try to do this on a daily basis until the infestation is under control.

Here's another article (http://botany.00server.com/AHktreehop0.html) which notes they are "tended by ants," so perhaps keeping your ants under control would help, too. Another site recommends spraying with soapy water, which shouldn't harm the plant.

Good luck!

Here is a link that might be useful: leafhopper article

Thanks Wanda and Susi. Indeed, the insects are the same as those in the pix in the link Susi posted (November 3 blog entry--leafhopper nymphs). They are everywhere in very large groups--the plant is way too big to do too much manually so I'll try some insecticial soap. They were there last year too but somehow the tree hangs in there through the cycles of having the new growth eaten way, regrows, eaten way, etc.

The good news is that I've never seen them anywhere else. And I have a lot of pest problems.

Thanks for your help. Kristine