I should say yes! They haven't ravaged mine but they have munched on the leaves to the point where there's a bunch of leaves with a bunch of holes in them. This seems to vary year to year. Last year my columnar European hornbeam had the worse JB attack but this year not so bad.

You could try an insecticidal soap spray, but most other things that you can spray are also harmful (broad spectrum poisons) to many others. Insecticidal soap can be made by mixing 1 teaspoon of a good and real soap (Ivory and Fels Naptha are two that come to mind), not a detergent, in 1 quart of water. This mixture must contact the target insect to be effective and looses its effectiveness when it dries.

In my yard in east Tennessee I found that the Japanese beetles feast upon my Montmorency and Lutowka Rose sour cherry (from Poland) trees, but the newer hybrid Carmine Jewel and Romance series sour cherry trees developed by the University of Saskatchewan, including Carmine Jewel, Romeo, and Juliet get pretty much left alone. But maybe that's because the beetles become full from eating the leaves from the straight Prunus cerasus trees. But it could be that the Romance series trees inherited some resistance genes from the Prunus fruiticosa (Mongolian cherry) parent.

slice - I always wondered about all the paintbrush pollination too (with respect to citrus). Some types of fruiting trees (and shrubs, perennials, etc) need pollination from a different flower to actually set fruit. But for citrus, most of which (save some like mandarins) are self-fertile, you don't need to really do anything. Within the flower, the pollen on the anthers will easily make contact with that same flower's stigma. Cross-pollination from other trees would generally help to make seeds (assuming the pollen is not sterile). In some cases, the tree exhibits "parthenocarpy", meaning they produce fruit with little or no seeds. Manual pollination would theoretically ensure the process but more often than not, you might end up damaging the stigma depending on how you jam a brush in the flower. If your tree is outside, the breeze and/or insects will help that process. Inside, you could always put a fan on it if you feel you need to do something. ALso "FP" = Foliage Pro in reference to a fertilizer product made by Dynagro - https://dyna-gro.com/foliage-pro