We usually get tons of japanese beetles in the summertime, but this year the population got cut way back by the late cold snap we had in spring. I'm not complaining one bit, either - first time our canna's have survived the summer.
BTW, get ready for a big stink when you take the full bags down and put up new ones. First time I did it, I tied up the bags to suffocate the beetles, and threw them in the garbage can in the garage. I came out the next morning to go to work, and stopped dead in my tracks in the garage and said "what the #$%^^ up and died in here??" Walked over to the garbage can, took the lid off, and about puked, it smelled so bad. Took three washings with bleach to cut the smell down in the can. I finally ended up putting the bag o' beetles in a plastic ziploc bag, putting that in an old plastic coffee can, and taping up the lid of the coffee can and throwing it in our outside garbage can. I don't know what causes decomposing japanese beetles to smell so badly, but DANG!! It's the worst thing I've ever smelled in my life.