What's That Bug? does not endorse extermination

Is this an Ichneumon?
I was taking some pics of some Giant Ichneumons ovipositing in a tree and this one was there too. Actually there were 2 of these on the same tree with about 3 Giant Ichneumons. It was just sitting there, but it’s the same size as a Giant Ichneumon but the "butt" is fatter than the others and the ovipositor a whole lot shorter, about a 1/4" long. Thanks!
Francine

Hi Francine,
This is a Pigeon Horntail, Tremex columba, a type of Wood Wasp. This female is depositing eggs that will hatch into wood boring larvae. It is relevant that you found the Pigeon Horntail depositing eggs on the same tree as a Giant Ichneumon because the Megarhyssa species are parasitic on wood boring larva. We found a Colorado State University web page with good information on both species that indicates the Giant Ichneumon is the most common natural enemy of the Pigeon Horntail. The page author, W. Cranshaw, writes of Megarhyssa macrurus: “The adult female can be seen searching the same areas used by the pigeon tremex, although they tend to be present a bit later in the summer. Developing horntail larvae can be detected under the bark by the female and she subsequently drills into the wood to the tunnel of the horntail larva. During egg laying (oviposition) the host larva is paralyzed with a sting after which the egg is laid. The parasitic wasp larva feeds on the paralyzed horntail larva, consuming it completely within a couple of weeks. It then pupates and remains dormant under the bark until the following summer, when the adults emerge. “

What's That Bug? does not endorse extermination
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