Good trap plants are four o'clocks (poisonous), larkspur (poisonous), castor bean (poisonous), borage, marigolds, light colored zinnias, and white roses. Some of the poisonous ones are also toxic to the beetles if they are eaten. Trap plants lure the beetles away from the target plants. You can selectively spray the trap crops with insecticides to kill them or you can go out and hand pick or vacuum off the beetles early in the morning when the dew is still out and the beetles have a harder time flying off.
It won't help immediately, but you can reduce the number of beetles over a couple of years by treating lawns with milky spore. Beetles will over winter as grubs in the soil.
Beetle traps have gone out of style but I used them for years. They will attract beetles from all around, reduces their number by 50%-75%. If your property is large enough set the traps out at the farthest corner away from the fruit trees. The beetles will be attracted to the lures there instead of to the trees and over time reduce the beetle damage, but expect an increase in the short run. I don't actually have Japanese beetles, but I do have Chinese Rose beetles which do practically the same thing except that they feed at night and I can use a light to control them. The Japanese beetle traps work well in trapping them, I just omit the pheromone lure. After a couple of years I hardly had any beetle damage and I was catching fewer beetles. The downside is that the lure will also trap bees attracted to the floral lure. It helps if you can get your neighbors on board with putting out traps in their yards as well. The traps should be put out about the time that the beetles start to emerge in your area.
Neem oil, is not my favorite thing, but it is an anti feedant and it works if you spray the trees before they become infested. Spraying should be every 3-7 days.
Happy gardening in Hawaii. Gardens are where people grow.