Japanese beetle traps work by using a pheromone to attract the beetles.  The are effective at attracting beetles but the concern is they my attract many beetles that may not have visited your property otherwise.  I have a colleague that gives a trap to his neighbor down the street each year.  Neighbor believes the traps help and the colleague believes it draws the beetles away from his property so it makes for a good relationship.  You may be further ahead by treating your yard for grubs.  Japanese beetles live part of their life as white grubs underground.  If you have a high population of white grubs a treatment may help.

This is the time of year that preventative applications for grubs can work well.  This will not get rid of Japanese beetles this year can can reduce the population for next year.