I have wondered about these so did a little search. From Wikipedia: In the adult form, it eats and damages leaves of many crops, including cucumbers, soybeans, cotton, beans, and many others. In the larval form, which is known as the southern corn rootworm, it tunnels through the roots of young plants, stunting or killing them. These native pests have a wide range of host plants, but will readily infest a field of crop plants, most notoriously corn.

Bayer Rose and Flower Care. JPs are smarter than they look. They somehow figure out that eating the leaves of the plant will kill them, so they tend to cluster around the flowers. However, this makes it a bit easier to use some of the other controls, such as knocking them in a bucket of soapy water or using the pyrethrin sprays. I typically only use this product on Roses, crape myrtles, and persicaria (the worst JP offenders in my garden). Pyrethrin sprays. These are generally packaged as generic insect killers or wasp/hornet killers in an aerosol can. Look at the list of active ingredients to find one. The only drawback is that tender young foliage may take a hit from these sprays, so be conservative with the spray until you know how the foliage will react. Also do not use on mandevilla vine. I used it this winter to treat mealey bugs on a mandevilla vine that I overwinter inside, and it promptly dropped all its leaves. Didn't kill it, but it came close.

More of the critters arrived to join the party, so they're now in buggy heaven (thanks to a few shots of Sevin). Although they couldn't hurt the hibiscus since it's finished blooming, they were right beside my confederate roses (that are now as tall as the house). They haven't started blooming yet.

Greengrower, I would get rid of the traps immediately. They just act as a beacon to every jb in your area. You'll never be able to catch enough to make a dent, plus, once they are in your backyard they are more likely to lay eggs in your soil, meaning more will emerge next year. Since you plants are potted your best chance is to dust them with Sevin, pick them by hand, and just plainly wait for their couple weeks to pass. I feel with you, as jb have made me rip out my rose garden and plant it with perennials they don't like. I also put down milky spores in my lawn area to fight the grubs before they emerge. I don't want to praise it too early, but it seems that after three years I finally seem to see less beetles. Mind you, they are still a plague, but somehow don't seem to reach the level where you want to use H-bombs. Also, I found out that by pruning back my Hibiscus syriacus bushes, their flowering seemed to be delayed enough to maybe make it passed the beetles. Maybe. Good luck!