Thank you for the question. Our publication "Japanese beetle management in Minnesota" describes the beetle's life cycle and possible control measures for the Japanese beetle grub and adult. According to the information, it is a bit too late to apply grub control now. The publication states that the presence of Japanese beetles doesn't mean you have a Japanese beetle grub infestation because the adults are strong fliers and will come in from great distance to find attractive plant material like your linden's.
Please read the article to find out what you can do next year to try to reduce the numbers of beetles on your property, but realize that you can't control the ones that fly in from next door!
The long term solution for all of us is to cultivate plants less attractive to the beetle in our landscapes and reduce the amount of watered and fertilized turfgrass the grubs need to grow and develop into adult beetles.
Thank you for contacting Extension.