Ovipositors

In one of my first posts, I wrote about some goldenrod rosette galls I collected and the things that were emerging from them.  I pointed out how this female torymid wasp could be recognized by her long ovipositor, which allows her to insert eggs deep within galls.

Female torymid, 2.8 mm.

Well, I just came across some photos I took in July that show a torymid–which may or may not be the same kind–that I found on a goldenrod rosette gall, putting her ovipositor to use.

In the next photo, you can see the actual drilling apparatus (stylets), angled forward, while the protective sheaths hang straight down from the end of the abdomen.

There are two stylets and two sheaths, even though each pair of valves looks like a single unit in the photo.  The presence of two sheaths is better seen in the following series, in which a giant ichneumon (Megarhyssa atrata) drills her outrageously long ovipositor deep within an old sugar maple to lay eggs in the tunnel of a wood-boring pigeon horntail (Siricidae: Tremex columba) larva.

Two female giant ichneumons (Megarhyssa atrata) home in on a horntail larva they have detected inside a tree.

Megarhyssa atrata, incidentally, is the largest known parasitoid wasp in the world, with the longest ovipositor of any arthropod.  The ovipositor can be up to 142 mm long, or more than 5½ inches.  The adult female of its host, the pigeon horntail, has a comparatively tiny ovipositor, although it is large compared with those of most other insects.  It is likewise used to bore into wood.  The one below has its stylets, visible as a black line, poking straight down into the wood, while the red sheaths remain in their normal position.

A female pigeon horntail (Siricidae: Tremex columba).

About Charley Eiseman

I am a freelance naturalist, endlessly fascinated by the interconnections of all the living and nonliving things around me. I am the lead author of Tracks & Sign of Insects and Other Invertebrates (Stackpole Books, 2010), and continue to collect photographs and information on this subject. These days I am especially drawn to galls, leaf mines, and other plant-insect interactions.
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10 Responses to Ovipositors

  1. Lisa Rainsong says:

    These photos remind me so much of the Conocephalus meadow katydids and the Oecanthus tree crickets I have been studying out in the meadows here in NE Ohio. So glad to have recently learned about your blog. One interesting insect just leads to another. I’m going to watch more closely for ovipositing wasps next summer.

  2. Ben Coulter says:

    Great post. I was unaware Megarhyssa atrata was the largest known parasitoid Hymenoptera.

  3. Dana says:

    Great photos and post!
    I was never fortunate enough to have a camera along when I encountered drilling ichneumons. Your photos reminded me of a question I always have when I see those long ovipositors…”What drilling method does their cutting tip employ? Rotary, as “drilling” implies? Or is it more like chipping or pinching through the wood?

    • Thanks!
      I haven’t found a good explanation of exactly what is going on mechanically. In fact, when working on this post, I’m pretty sure I came across a statement that no one really knows what’s going on. Whatever it is, it takes a while–the photos here span 12 minutes, and I don’t know how much longer she was at it after I left.

  4. Marvin says:

    Great shots of the Megarhyssa atrata.

  5. Pingback: Gall Wasp Parasitoid | BugTracks

  6. Paulette Smit says:

    My dead hickory tree is full of those megarhyssa atrata wasps. Do I have to be concerned about anything? I live in Wisconsin.

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