Ant bait. I use terro. There is a terro for outdoor use. You can also put a barrier on the tree. I use vaseline and make a 5-6 inch band around the trunk of the tree near the base. Then I spray the vaseline with boric acid. It keeps the ants from climbing up the tree for a while. You can also use tanglefoot.
Hose down the foliage with a jet of water to dislodge the citrus aphids. They are usually a problem when the tree is putting on new growth. If you want to try to get ahead of the problem start spraying with neem when the tree starts to flush with new leaves.
Greenhouse frogs, lizards and toads eat ants. Killing the workers is futile, that is why terro works better. The ants will take the bait back and feed it to the queen. I replace the bait every couple of months. Ant colonies here can have multiple queens and I sent my ants to the Department of Ag and they said I have at least two different species of ants but all of them are sweet eating so Terro works. For grease eating ants you need to use a peanut butter based bait.
This is a publication from the Hawaii ant lab it is about fire ants but the bait works for any grease eating ants.
https://www.littlefireants.com/08%20LFA% ... 0Sheet.pdf