What are these and how do I get rid of them? I have a 10 year old Black Walnut tree. It started dropping immature walnuts with small brown holes (pictures attached). I cut two of them open and found this grub inside. another picture shows the cross section of the hole. I want to get rid of the insects this year or prepare to get rid of them next year. This is the third year the tree has produced walnuts. I lost several immature nuts last year but did not notice the holes then. Please advise.
Kent County Michigan