The Friends of the Public Garden, along with its partner The Highland Street Foundation, hosts a volunteer opportunity on the Boston Common Wednesday, June 23, beginning at 3 pm. After attending a training session, volunteers will use maps created from a tree inventory to look for evidence of the longhorned beetle in trees on the Common. A reception at the Parkman House to thank the Highland Street Foundation for funding the inventory will follow. Free. For more information log on to www.friendsofthepublicgarden.org.