These cocoons on the underside of an ash leaf, appear to have been opened and the pupae eaten. Maybe the wasps left of their own accord, but these cocoons seem to have been torn open, as for food. When I think of exit holes made by wasps I think of neat, tidy, little holes not these messy things. But who knows? Perhaps the Chalcidid wasps are so eager to emerge that they forgo neat and tidy!