I found this:
Control of the locust leafminer is generally not necessary. ... The locust leafminer is primarily a pest of black locust. Adults skeletonize and eat holes in the leaves; whereas, larvae mine the tissue between the upper and lower-leaf surface (mining damage is the most destructive). Under outbreak conditions, whole hillsides turn gray or brown, often suggesting fall color change. Outbreaks of the locust leafminer are generally more spectacular than destructive. In combination with other stress factors, outbreaks contribute to growth loss and occasional tree mortality.
https://na.fs.fed.us/spfo/pubs/pest_al/l ... lminer.htm
Their point is that the damage is generally more cosmetic than causing long term harm to the tree, unless a sever outbreak of the leafminers is paired with other stress factors like drought.
Similarly:
The adult beetle feeding has little affect on the tree health. However, the mining by the larva can cause growth loss or death in trees under stress. Typically, parasites and predators will reduce the leafminer populations and chemical control rarely is warranted.
https://www.state.sc.us/forest/idleafminer.htm
There are several parasites and predators of the locust leafminer which may explain why it does not maintain large populations in one area for a long time.
https://ipm.ncsu.edu/current_ipm/01PestN ... ament.html
This is the closest I could find re what those "parasites and predators" are:
everal natural control agents including parasitic wasps and predators such as the wheel bug prey on various life stages of the locust leafminer.
https://www2.ca.uky.edu/newsreleases/2000/Jul/locust.htm
I would guess those parasitic wasps are at least relatives of the little braconid wasps which parasitize my tomato hornworms. (Today I found two tomato hornworms and both of them had already been heavily parasitized and were dying or dead.) If so, then the adult wasps eat flower nectar and pollen. To attract them, grow flowers that have nectar in lots of little florets like parsley dill etc when allowed to flower,chamomile, buckwheat, wild grapevine and others.
Do I have anything to worry about? Is there anything I can do to safely control or prevent the situation next year? Someone recommended Bayer Advanced 12 Month Tree & Shrub Protect & Feed II... any idea if this is safe to use?
)
Planting things like dill and parsley and letting some flower really does work in attracting lots of beneficials. I just noticed that sedum is another one of those things with the tiny nectar bearing florets. Mine is blooming now and it is swarmed by a whole variety of bees, bumblebees, teeny-tiny flies, and other stuff. If there were braconids in there, I didn't spot them, but they are less than 1/4 inch long and hard to spot.