Any ideas what’s going on with the leaves on this mandarin orange tree?
Leaf miners. They are not harmful in small numbers. Spray spinosad in the evening to control them.
Leaf miners cause curling but it may not be leaf miners because I do not see any channels within the leaves. Aphids cause curling of new leaves. Check for aphids and, while you are at it, check for spider mites.
Post some pics of the leaves.
Lots of leaf miner channels in the leaves. That’s not to say there won’t be aphids or spider mites.
I see channels,when photo is enlarged.bb
I think I found the problem. Some sort of probably moth larvae brownish red with a white head about 1" to 1 1/4" long on several of the trees leaves. Close to ten of them found on my 7 trees. Trees seem to be recovering now. They are regrowing leaves where the consumed and damaged leaves were. The closest thing I could find that looks like them is this: Giant swallowtail, Papilio cresphontes (July 6, 2013) — Texas Insect Identification Tools
Your problem is leaf miners. They are very small. Can’t say I’ve ever seen the actual moth they are so small. Leaf Miners - mrtexascitrus
There may also be leaf miners. I’ll still plan on treating for those. I for sure had the swallow tail larvae eating the leaves. I picked close to ten of them off the trees. I actually saw them when I took the picture for this post, but thought it was bird poop on the leaves. LOL