The Japanese beetle was first discovered in the United States in 1916 near Riverton, New Jersey. Since that time it has spread from Maine to Georgia and westward to Illinois, Michigan, and Missouri. It reached North Carolina in 1932, but did not reach Tennessee until about 1990. Considering that the beetles are strong fliers, and that they left most of their specific natural diseases, parasites and predators behind, it seems that the quarantine efforts used have been an impediment to the spread of Japanese beetles across the United States.
When used properly, Japanese beetle traps can suppress Japanese beetle populations up to 30 percent if a large enough area is trapped (perhaps a whole neighborhood). This is not enough suppression, however, for most homeowners and landscapers. Additionally, Dr. Dan Potter at the University of Kentucky has shown that in a specific yard, if none of the neighbors are using traps, it is sometimes WORSE to have a trap than not. The problem is that the traps are so much better at attracting the beetles than actually catching them that you wind up with more beetles in the vicinity of the trap than in the trap. This is especially true if the bags are not emptied regularly. Once the beetles begin to rot in the bag, ammonia repels live beetles from the immediate vicinity of the trap. However, the bait keeps on “calling” the beetles for a much greater distance than the ammonia repels them. The net result is far greater plant damage than would have been the case in the absence of the trap. If you use traps at least place them away from plants that are to be protected and empty them every day or two.
Sevin and other insecticides are labeled for Japanese beetles and will do a good job of controlling them as long as the residue remains on the plant. A problem with Sevin is that honey bees may gather the residue like pollen and carry it back to the hive to feed their larvae. It is recommended that persons NOT try to control Japanese beetles on flowers for that reason (and it is against the product labeling). Also, flowers open so rapidly that a bud sprayed in the morning might be open by afternoon and the beetles could then attack the petals because the residue is on the sepals below. **With any pesticide, read the label and use only as directed on the label.