Ask Mr. Smarty Plants

I think the black and orange bug you have is a type of Pleasing Fungus Beetle, probably the Red-banded Fungus Beetle, Megalodacne fasciata that typically feed on bracket fungi, Ganoderma spp.  The bugs themselves are likely only interested in the fungus and pose no harm to the ash tree.  Ganoderma is a wood-decaying fungus that has no cure and will eventually kill your ash tree - though this could take many years.  Since visibility of the brightly colored fruiting body is often indicative of advanced root decay and structural instability, you may want to have the health of the tree evaluated by an arborist if the tree is in a location where it could harm structures or other trees when it falls.  Trees are often infected by fungi when the trunk or lower roots are wounded.  This fact sheet, How to Care for Tree Wounds, by the Ohio State University Extension provides information that may help you prevent other trees on your property from contracting fungal infection.  If the tree is not in danger of harming anything else when it falls, you might enjoy taking the 'live and let die' approach.  As the Pleasing Fungus Beetles you noted are clear evidence of, trees in all stages of decline and death are a rich part of natural habitat and attract a myriad of creatures and insects who rely on them for food and shelter.