Answer: There is nothing you need to do for them this late in the season, the leaves have for the most part already done their job for the year. Unfortunately, Japanese beetles are strongly attracted to these trees.
The Japanese beetles are Japanese beetles are difficult to control, in part because they fly long distances. The pheromone traps are not recommended because they actually seem to attract more than they catch.
You can try to repel the beetles using a spray containing neem, or you can handpick them (they are sluggish early and late in the day). Or, you can spray with spinosad or with carbaryl (the active ingredient in Sevin) but keep in mind this is a contact insecticide with no residual action. Also, it can be difficult to spray trees once they grow large.
You can also use beneficial nematodes or a neem based product sprayed on the lawn in late summer to early fall to kill them at the grub stage. (October is too late to do this.) Milky spore disease in granular form can also be applied to the lawn any time the ground is not frozen and a treatment lasts in the soil for many years, but it takes some time to see results. Be sure to read and carefully follow all of the label directions on any product you use.
Unfortunately, most gardeners find they have to tolerate a certain amount of damage, and some years are more severe than others depending on the weather and other conditions.
You might be interested in reading the following recent release from Penn State about using alternative methods to control the grubs.
I hope this helps.
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