How do I look for it?
How do I find psyllids? Check your citrus trees monthly. Whenever you see tiny new leaves forming (leaf flush), look closely for signs of the psyllid. Remember the adults fly and so they may be hard to observe and the eggs are so tiny they are hard to see without a hand lens.
Young nymphs can only survive on the soft, tender leaves and twigs. Its best to look for the nymphs because they are concentrated on the new leaves, they don't move very much and they produce waxy white tubules that can be easier to see than the insects themselves.
A lot of ant activity up and down the trunks of trees and in the foliage is often an indication the tree is infested, though not necessarily just with ACP. Argentine ants will tend other sap-sucking insect pests too.