I have had previous experience with them, about ten years ago when they invaded my garden at a house I no longer live in. I had no clue on what to do about them, but I had to try something. They had eaten most of my plants in my back flower beds and vegetable bed and were chomping their way to the ornamental bed at the front of my house. The first line of attack was of course pesticides. Some are known to work well against the adults, such as Sevin®, but I dislike using pesticides, at least until I've tried other remedies. Some websites gave lists of resistant plants, which is great when you're choosing what plants to plant but when the Nipponese Nibblers infest a long- established plant it doesn't do much good. There's also the manual removal method. With a pencil, prod the devils off the plant and into a bucket of soapy water, the brochure told me. This method does work, but who wants to tickle beetles off of a plant in the middle of summer, especially when there can be hundreds of the devils on just one plant? So I resorted to the 'Bag-A-Bug' traps sold at the local Wally World and other such stores.
The Bag-A-Bug traps work on two principles:
Principle #2 - As these bugs aren't really all that intelligent and also somewhat clumsy, the Bag-A-Bug system uses these bug traits to full advantage to trap them.
A close up of the Bag-A-Bug system:
As with most things, experience proved to be the best teacher with these traps. For example, the sexual pheromone 'bug porn' that turns them into sex bandits ravenous for a roll in the hay is enclosed in plastic that has to have a peel-off paper removed. Be advised, do not, I repeat, DO NOT put this peel off paper in your shirt pocket! There is enough of the pheromone left on the paper to make the bugs think you're not a bad looking bug yourself. Take it from somebody who found out the hard way, to be covered by a swarm of humping Japanese Beetles is not a pleasant experience.
There are some pitfalls to these traps. As the pheromone is very potent and the beasties can detect it from way far away, the traps do attract a lot of bugs. Let me emphasize that - these traps attract A LOT OF BUGS! If you are repulsed by the sight of swarming bugs with but one thing on their mind, perhaps these traps aren't for you. Personally, I take heart in the fact that while I may be leading bugs to their doom, I am ensuring them they will die sexually satiated. Not a bad way to go, especially for a bug. Also, change the bag after two days or so even if it isn't full. The stench of dead bugs in the bag can be smelled by live bugs and will counteract the pheromone, not to mention turn the stomach of the strongest intrepid bug hunter.
There are detractorsthat say these traps attract far more bugs than they capture. That may be so, for I don't keep a running count of visitors to the trap and those who actually end their days in the bottom of the bag. Suffice to say that the one other time I used the traps at my other house, I caught twenty bags of bugs over a 4-week period, and it made a big enough dent in the bug population that they were not a problem at that house for the rest of the ten years I lived there. The objective is to not only kill the adults that are feeding on your plants, but to prevent them from laying eggs in the ground that create next years' problem.