Pesky Parasitoids, Part 2

Back in August I gave a talk and co-led a walk at an event in southern Ohio called “On the Trail of E. Lucy Braun”, a celebration of the life and work of a renowned Ohio botanist and conservationist. I was there, of course, to make sure Lucy’s sister Annette was properly represented. The walk took place at Lynx Prairie, a site the Braun sisters visited regularly. On August 25, while we were scouting for the walk, Julia spotted a single mine of a Brachys larva (Buprestidae) in a leaf of hophornbeam (Betulaceae: Ostrya virginiana).

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This beetle genus is primarily associated with oaks, apart from the recently described Brachys howdeni on trailing arbutus (Ericaceae: Epigaea repens). Any larvae found on other host plants are of particular interest as Henry Hespenheide works to  revise this confusing genus, and hophornbeam was a new host record as far as I knew. So I kept a close watch on this larva after we collected it, struggling to decide whether it was better to preserve it for DNA barcoding or attempt to rear it to an adult (which was by no means guaranteed to succeed, and would involve waiting until spring).

On September 1, I was dismayed to discover an ectoparasitoid attached to the larva:

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So the decision was made for me. As we saw in my previous post, I didn’t have much time to lose before there was nothing left of the larva. I tore open the mine, giving me a better view of a parasitoid larva than I normally get to see…

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…and then I wrested the parasitoid away from what was left of the beetle larva, plunking the latter in a vial of ethanol so I could try and get a DNA barcode from it later. I offered the wasp larva a Brachys larva from another host plant, but it showed no interest in it. Instead it wandered the rearing vial forlornly for several days, finally settling down to pupate on September 5. My pictures of the pupa aren’t great because the first was taken through the wall of the vial, and the second was taken at an awkward angle looking down into the vial.

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As you can see, this larva deposited liquid meconium rather than the apparently solid pile left by the Stigmella parasitoid. Between ten and twelve days later, the adult emerged (while I was away at the Berkshire BioBlitz, so I didn’t get to see it alive).

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I suspect she’s another Pnigalio (Eulophidae) of some sort, but time will tell.

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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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4 Responses to Pesky Parasitoids, Part 2

  1. AlexW says:

    Why have adult insects frequently been found dead when being reared? Do they typically perish of “old age” or improper living conditions (starvation, dessication, etc.)?

    (I don’t mean fatal mismolts; only situations like this post’s, where the adult seems completely normal)

    • It’s not always clear, but this one was likely some combination of starvation and desiccation–always a risk when not checking rearing vials for a few days.

      • AlexW says:

        Would wet cotton/paper help?

        I’ve heard repeatedly that commercial “beetle jelly” (for the Japanese pet beetle hobby) is quite rot-proof and can be used for weeks/months in a beetle cage. I have seen preservatives listed in the ingredients of at least some brands. They seem rather expensive for feeding micro-insects, but rationing small chunks to them may possibly be useful when valuable specimens are involved.

        • Yes, some humidity certainly prevents desiccation, and I probably had a damp piece of crumpled-up tissue in this vial as I normally do, I just don’t remember the exact situation since this was three months ago. I don’t know what an adult parasitoid like this needs to survive, but there wasn’t any kind of food for it in the vial. I don’t ever have insects die like this when I’m checking the vials every day, so I haven’t had any need to look for solutions like what you’re describing.

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