Flies in peony stems

phlowerpower(5)June 29, 2014

The cut tips of several peony stems had signs of borers--I could see the inside material of the stem powdered and on the lower leaves. I split a stem in half and found several small flies inside the stem. They showed no sign of life. I am pretty sure they are small flies--they have the typical fly shaped wings and large eyes. I am just so curious to learn more about the life cycle of these flies. I have about 6 more peony stems with the same signs of borers. Anyone know what they are?

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jean001a(Portland OR 7b)

Oh, how interesting. You have a great example of biological control in action!

This is a relatively common phenomenon in which a predator insect hollows out the soft pithy center of a stem in order to lay its eggs.

Do you see the tan "plug" at the far left and another towards the right? That's evidence of a small predator wasp which is stocking each cell (the space between 2 plugs/partitions) for its youngsters. The prey are alive, but stunned, and will provide fresh "food" for the predator's young.

One cell per youngster. Many prey per youngster; with more prey for females than for males.

I'm curious where you live. Please tell us city & state.

    Bookmark   June 30, 2014 at 12:06AM
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I was thinking it looked as though these flies were being stocked up by some other creature. Ok I am off to look up more info about wasps doing this. I live in Iowa. Thanks for the reply!

    Bookmark   June 30, 2014 at 4:39PM
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rhizo_1 (North AL) zone 7

Fascinating, jean! This one really had me scratching my head. The image was perplexing, to me. Any idea what genus of wasp this might be?

    Bookmark   June 30, 2014 at 6:47PM
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jean001a(Portland OR 7b)

No I don't.
And I would like to know if the prey truly are flies. I can't see enough detail to be certain.

Okay, this is the back story. I have a friend who is a fanatic about monitoring & documenting mason bees in the local Master Gardener demo garden.

And since he started, he has seen several predatory wasps also using his bee nests.

If you're interested, reserch these:
- Isodontia elegans, common name the grass-carrying wasp -- a wasp about an inch long; prey are tree crickets
- Passaloecus species -- a very small predatory wasp; prey are aphids

This post was edited by jean001a on Tue, Jul 1, 14 at 17:25

    Bookmark   July 1, 2014 at 3:29PM
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Here is a photo of one of the insects in the stem. Has fly shaped wings and eyes as far as I can tell.

I am only seeing signs of activity in my cut peony stems. So fascinating! I haven't spotted the creatures doing this though.

    Bookmark   July 2, 2014 at 4:09PM
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jean001a(Portland OR 7b)

I think you're correct. Can't see antennae but can discern the shape of the head.

    Bookmark   July 2, 2014 at 7:13PM
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tsugajunkie z5 SE WI

Thanks to folks like Jean (and rhizo, for that matter), I never stop learning. That's a new one for me.


    Bookmark   July 2, 2014 at 9:34PM
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