I have these here too. Are they shiny black with no other colors? Are the grubs a little smaller than other grubs? It might be Black Turfgrass Ataenius. They do a number on zoysia and bermuda as well. First noticed them back in the 1990's. My weapons of choice are no longer legal on lawns. Now I make do with a high volume application of permethrin. It is worth it to kill the adults because they are overwintered adults that are going to lay eggs for the next generation of grubs. Unlike Japanese Beetles, these do not feed on plants. They only come out to lay eggs that turn into grubs. Lawns that have this need to be on imidacloprid applied in spring. I do not have seasons so the two are tank mixed and drenched when I see the adult beetles flying around at night.
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Benjamin Franklin 1775
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Benjamin Franklin Poor Richard's Almanac1738