I believe that these are Ichneumon wasps. We watched them for quite some time as they took turns laying eggs. The "fan" at the tail was iridescent and pulsating. Thanks!
Congratulations on your stunningly beautiful image of two female Giant Ichneumons, Megarhyssa atrata, ovipositing. We especially love the tiny centipede visible under the bark. We do not fully understand the mechanics governing the ovipositor, but this membrane is visible on numerous photos in our archives and elsewhere.