Punctured leaves Minimize

April 2009. Yams (Dioscorea alata) in New Caledonia are seen with black puncture marks on the leaves. Symptoms are seen on the older leaves. In some cases, ants can be seen visiting them. Each puncture has a bright centre surrounded by a necrotic area. Has anyone seen this before and knows the cause?

No one had seen such marks on leaves of yam, but it was thought the punctures were feeding marks, possibly by a mirid bug.