The Adult Japanese Beetles are a problem for about 6 weeks during the summer, although you could get the idea that they are around for much longer. While certain plants do appear to be magnets most often they are attracted to plants that are stressed for some reason and it may not always be easy to determine why the plants are stressed. Take all the environmentally correct means to control these wee buggers and look closely at those plants to try and determine why the beetles may be more attracted to them.
1. Are they planted in an area that is similar to the native habitat of that plant?
2. Does the plant get the nutrients from the soil needed for good health?
3. Does the plant get sufficient water for its needs?

Kimm, I'm sorry, but "most often they are attracted to plants that are stressed for some reason" is just not right. I wish you would stop saying this. The Japanese beetles in my garden are most often attracted to the rugosa roses and the raspberries, and the rugosa roses and the raspberries are healthy as can be. You don't have Japanese beetles in your garden, do you? What is your first-hand, personal experience with Japanese beetles?

Frances, in my opinion [but I haven't done any official scientific research on the subject :-)] having plants that the Japanese beetles love won't affect next year's Japanese beetle population noticeably. The Japanese beetles on your crape myrtles don't come from just your yard, but your neighbors' yards, and their neighbors' yards, and...

I also don't agree about stressed plants attracting JB. They go for what they like, no matter how healthy it is. (In my garden their favorites are basil, grape, hollyhock, wild evening primrose, wild berries.) We knock them off into containers of plain water and flush them down the toilet, and have also been known to vacuum them. They do diminish over the years if you're diligent. Also, drought conditions seem to discourage them, something about their not being able to hatch properly. We tried traps for a while and only ended up attracting every JB in the entire neighborhood. Once we stopped using traps our population decreased dramatically. I wouldn't get rid of the crepe myrtles yet if I were you. Next year may be much better!
Good luck.

At this stage of the season the JBs here have moved mostly to the blossoms of the hibiscus.....because they love them. In fact they love the white blooms much better than the darker colors....not because of stress but because they love them more.

The Japanese Beetles are not on my Hibiscus, which is now in full blossom, but they are on some hollyhocks that self seeded in some soil that I have not done much with the last couple of years, the hollyhocks show signs of stress. They have visited some other plants but leave fairly quickly seeming to prefer the sand cherries and Purple Leafed Plum, that are planted a bit higher then they should be and are stressed, now, because of low water levels.
There are a number of really good researchers that have found that plants under stress are more attractive to insect pests then are plants that are growing in a good, healthy soil.

Thanks to everyone for your responses. Although disappointed that they enjoy these crepe myrtles so much, I feel better about it not increasing them for next year. I really like these trees and am going to keep them! Thanks again for sharing your opinions and experiences - hearing from others helps to sort things out. Thank goodness those devils are about gone for this year!

Frances

I was thinking about the stress factor today when I was out knocking Japanese Beetles off my very healthy basil. Maybe part of our problem is a logical fallacy. JB may be attracted to stressed plants, but their presence on a plant doesn't necessarily mean the plant is stressed. ? Oh, well. Just a thought.

A good thought, weld. If you will notice, the JBs like the new tender soybean leaves on the healthier plants while leaving the less healthy plants alone for the most part.

Thanks, Wayne! I truly believe JB ,and probably most other insects, have definite preferences. For example, JB don't like lemon basil. I'm sure they'd eat it if there was nothing else around, but in my garden the lemon basil is planted right next to the sweet genovese type, and both are equally healthy stands. The regular basil is full of Japanese beetles, the lemon basil, not 4 inches away, has nary a beetle. Years ago I noticed that slugs prefer certain lettuces (bibb types being the fav), and aren't crazy about red lettuce. So I began planting red lettuces around the other lettuces like a fence. It worked!
By the way, I'm feeling a bit guilty that krikit's thread got off her /his specific topic. I hope you've found something helpful, krikit! Best of luck.

Like others have said, the JB population changes from year to year. Last year, they skeletonized my grape vines and ate all the silks off my corn. I still got a harvest from both, but the corn ears weren't completely filled out.
This year, we are in an exceptional drought, and I probably could have held all the JB's I saw in the palm of one hand. The only thing they messed with was my Crepe Myrtle and Wisteria Vine that formed a symbiotic relationship long before I bought this place in 1984.
The JB's were gone in 3-4 weeks and everything has recovered. Best double crop of corn I've ever had and grape vines are hanging full. Benign neglect sometimes works. Good luck to you.

Steve, sounds like we may be neighbors. Severe drought here, too, for 2 years. I'm all in favor of benign neglect, been following that principle for years, and also acceptance of the vissisitudes . (That doesn't look right.) I've plucked probably 200 Japanese Beetles this year,despite the drought, and envy your handful, but it used to be much, much worse! I'm pleased, very pleased, with 200. (Oddly, we moved into our place in 84, too.) Let's hear it for benign neglect!
Best wishes, weld.

Spelling correction. :)