Yes, you are correct. You have Japanese beetle. Sevin will work to kill the beetles, but they have an aggregation pheromone, so they will keep coming back even with the spray. It will kill what is on the tree though... Sevin will kill bees too, so if you are worried about your bees, you are better not to spray. You can pick them off, but again, they will keep coming. They are likely coming from your lawn or expanse of grass/turf close. You could target the grubs as they feed on grass roots in the soil. Grub X is a great material, but it would have to be put down in the spring when the grubs come back to the surface to feed on the grass roots. Now, the adults are mating, and the females will lay eggs. Eggs will hatch and the larvae will feed a bit, but then they will move down into the soil to overwinter. Best time to target the grubs is spring when they come up to feed again.

I think that you are losing fruit to birds or squirrels. Bird pecks are common, and they will leave the pits hanging from the stems. There will be partial cherries left once birds move in. They usually don't take the whole thing which is more likely squirrels. I don't see squirrels in orchards much, but if you leave in a more suburban place, it is possible. Birds are my guess though... as soon as fruit gets sugar or color, birds hone in, and if you only have one tree, they can clean you out in hours. 

Japanese beetle will feed on developing peach fruit, so you could net the fruit with small bags to protect it. Again, I think picking off the beetles would be effective if you have the time. The only good thing about JB is that they don't last too long... they should be finished eating and mating in three weeks.

Hope this helps a bit.

Nikki Rothwell