plum tree leaf curl

The only pest that is written about is aphids, which I see in my first and second photos. And the black-and-red beetles that fly around the branches in my 3rd photo must to be Soldier Beetles https://agsci.oregonstate.edu/nurspest/insects/soldier-beetle

It's always surprising to see infestations despite plenty of predators present. I have a major earwig infestation for the last 15 years, but that doesn't prevent aphid infestations on my garden greens either.

I do have a lot of ants in the yard.

The ants are probably a big part of the problem honestly. They farm the aphids and protect them from predators, so even with soldier beetles around the aphids still thrive because the ants are running interference. If you can deal with the ants the predators tend to clean up the aphids on their own pretty quickly. A sticky band around the trunk stops them climbing up, that made a noticeable difference on my fruit trees.

I haven't seen ants on the trees, but maybe I don't know enough of what to look for. I'll read about the ants and try to reduce their population. They are increasing every year all over the yard in the ground and in some pots.