Japanese Beetles, Popillia japonica, were first discovered in this country by Harry B. Weiss and Edgar L. Dickerson in August, 1916, while they were inspecting the nursery of Henry A. Dreer, Inc., about two and one-half miles east of Riverton, New Jersey, probably imported in the grub stage in iris roots which the nursery had imported from Japan five or six years before.
The Eastern US provides a favorable climate, large areas of turf and pasture grass for developing grubs, hundreds of species of plants on which adults love to feed, and no effective natural enemies.
The adult beetles normally emerge during the last week of June through July. The first beetles out of the ground seek out suitable food plants and begin to feed. These early arrivals begin to release pheromone that attracts additional adults. After feeding and mating for a day or two, the females burrow into the soil to lay eggs at a depth of 2 to 4 inches. Females lay 1 to 5 eggs before returning to plants to feed and mate. This cycle of feeding, mating and egg laying continues until the female has laid 40 to 60 eggs. Most of the eggs are laid by mid-August though adults may be found until the first frost.
In case that first bullet of information was confusing...here it is in simplest terms...
ALL THEY DO IS EAT AND MATE AND LAY EGGS!!!!
ALL DAY EVERY DAY!!!
Yeah right...I have nothing better to do than walk around the yard and hand pick the 15,000 Japanese Beetles that are currently "living" in my yard. If this option is attractive to you note they are less active in the early morning or late evening. They can be destroyed by dropping into a container of soapy water. (I would find it much more satisfying to use liquid nitrogen and then get the satisfaction of smashing them on the ground into a million small fragments!)
The adults do not like to feed on ageratum, arborvitae, ash, baby's breath, garden balsam, begonia, bleeding heart, boxwood, buttercups, caladium, carnations, Chinese lantern plant, cockscomb, columbine, coralbells, coralberry, coreopsis, cornflower, daisies, dogwood (flowering), dusty-miller, euonymus, false cypresses, firs, forget-me-not, forsythia, foxglove, hemlock, hollies, hydrangeas, junipers, kale (ornamental), lilacs, lilies, magnolias, maple (red or silver only), mulberry, nasturtium, oaks (red and white only), pines, poppies, snapdragon, snowberry, speedwell, sweet pea, sweet-William, tuliptree, violets and pansy, or yews (taxus). Nice list...and I like growing many of those things... but if you fancy growing roses, hollyhocks or hibiscus...you're a beetle magnet. Their actual "Love to Eat" list is too long and depressing to post...just take a walk in your yard...it will be abundantly clear. (sigh)
Those cute little "Bag a Bug" traps you see hanging in peoples yards...forget them. Traps tend to attract more beetles into the area than would normally be present. YIPPEE!
Oh so politically incorrect, but effective.... acephate (Orthene), carbaryl (Sevin), among others... not advocating...just putting it out there as a possibility.