J. Beetles are the adult of grubs. Chemical treatment with Merit or other. Organic treatment is Milky Spore. Here is a link that might be useful: Durn Pests

I think you are referring to Japanese beetles, they are stout greenish metallic. Unfortunately,there is no really effective way of dealing with them. Some snip all the buds and blooms off during the beetle season (June and July in my zone) because they ruin them anyway. Pesticides really don't work because they have to ingest it therefore consuming your roses in the process and killing bees and beneficial insects. I (and many here) go out several times per day and knock them off the flowers into a container of soapy water(soap added is the key,otherwise they can swim for days!) You won't get rid of all of them but it will help control the population. Others report milky spore applied to your lawn will decrease numbers by killing the larval stage-grubs, but it takes a couple seasons to see a noticeable difference. Avoid japanese beetle traps sold at retailers, they are reportedly so effective that they attract even more beetles to your yard to munch on your plants.Okay, long response but these are my most hated pest! In short,drown them and get rid of flowers for the short term.

What I would do is apply a couple of good coats of Surround ® WP, a kaolin clay product that makes a slurry when mixed with water according to the directions. It will coat the fruit with the clay, making them unpalatable to chewing, sucking, boring, and egg laying insects and arachnids. It also protects against sunscald and heat stress. It's completely organic and safe for edibles. It does form a film that will need to be rinsed off before eating but I have found it very helpful with pests in my garden.

I also don't think dethatching will make a difference with grubs... Somewhere I remember reading that in areas where the summer dries out the lawn, beetles are much more likely to lay eggs in lawns which are watered and green rather than a browning yard (mine). Hmmmm. A brown lawn from grubs or a brown grub-free lawn. Tough choice although I chose the cheaper not watering option! My neighbor always puts down grub killer and I'm then faced with masses of dead earthworms coming up out of the lawn. Then he complains about how much thatch he has. I tried to explain how the earthworms feed on thatch and that he kills them every spring, but I guess he's just too afraid of grubs.