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Flies? (found on the underside of a rock in a coldwater stream)

Flies? (found on the underside of a rock in a coldwater stream)
Shelburne, Dufferin, Ontario, Canada
July 1, 2006
Size: <10 mm?
Sorry for making it look like all five images are of the same specimen. I'm still learning how to use BugGuide. It won't matter since none of the images are "keeper" quality - they will all be frassed after i.d.

Images of this individual: tag all
Flies? (found on the underside of a rock in a coldwater stream) Flies? (found on the underside of a rock in a coldwater stream) Flies? (found on the underside of a rock in a coldwater stream)

Moved from Insects.

per our conversation below, I just noticed that Malcolm Storey's website (UK) mentions two entomophagous fungi that infect adult caddisflies: Erynia conica and Erynia rhizospora.

I wonder what is known about their life cycle. I'm curious now, maybe I'll pursue that at some point.

Erynia rhizospora
I found a reference to "adult Trichoptera held firmly beneath logs and stones around rivers by rhizoids [rootlike structures] of Erynia rhizospora" in:
Roy, H. E., D.C. Steinkraus, J. Eilenberg, A.E. Hajek, and J.K. Pell. 2006. "BIZARRE INTERACTIONS AND ENDGAMES: Entomopathogenic Fungi and Their Arthropod Hosts." Annual Review of Entomology 51:331-57.

Based on this page, Erynia conica seems to be a generalist, attacking true flies and aphids as well as caddisflies.

I still haven't found anything describing the life cycle, but we now have an interesting series showing how this fungus progresses:

The White Death
what a tragedy... look rather like caddisflies to me; i'll show it around

These look like...
caddisflies to me as well--perhaps something like Psilotreta, although that is strictly speculation. To speculate further, the best scenario that I can come up with is that an eddying current accumulated them against the rock after oviposition (the semi-spent wings seem to suggest that, although perhaps they were trapped there when someone/something stepped on the rock), and fungus grew on the damp, dead bodies.

I would disagree with that assessment. This has the classic look of a pathogenic fungus, likely specific to caddisflies, that bursts out of insects' bodies (especially between abdominal segments) and attaches them to a substrate. For some similar images, see here (in particular the "fungus-ridden flies" link).

Sorry, Charley...
I know nothing about fungus, pathogenic or otherwise, and trust your assessment of that. I was mostly trying to figure out how an accumulation of adult caddisflies might be found under a rock. Some species crawl out to emerge and some crawl/swim underwater to oviposit. (Although, if these were Psilotreta, that would not be their emergence or egg-laying habit). However, I mostly see accumulations like this collecting in places where they are washed by the current after oviposition.

I assume from what you are saying that the fungus would have been the cause of death rather than something that consumed the caddisflies postmortem. Can you tell me any more about the possible mechanism of such an infection?

No problem...
Yes, the fungus would be the cause of death. I've never read anything about fungi that infect caddisflies. The ones that infect grasshoppers and flies cause the victims to die in prominent places (grasshoppers climb to the tops of stems), which gives the spores a better chance of dispersing. Infection is simply from spores landing on the host and germinating. There are other dispersal strategies--there is one that infects periodical cicadas and causes their abdomens to fall apart piece by piece as they continue to fly around as if nothing is wrong.

Whatever the mechanism, it is clearly possible for fungi to cause abnormal behavior, such as Psilotreta adults wandering onto the undersides of rocks to die. This induced behavior makes me wonder if this fungus infects caddisflies as larvae, with the spores dropping into the stream, but that's pure speculation and I don't know if it's possible for fungi to disperse in water. I wouldn't be too surprised though, they seem to be pretty clever.

Thank you
I have seen periodical cicadas that were infected in the way you describe. The possibility that the infection could cause abnormal behavior is fascinating.

How much less than 10 mm? Psychodidae (Moth Flies) might have adults coming to lay eggs on algae, then die and fungus does the rest?

Okay, I just jumped into this
Okay, I just jumped into this fascinating discussion. The flies were only slightly less than 10 mm, including the fungus. There were large accumulations of them on the underside of semi-submerged boulders in a coldwater stream. Judging by their location away from any eddies, I am confident that the flies congregated under the rock and then died, and were not swept into place by the current. I've added a couple more photos. Foam is visible in one photo which might indicate an eddy but in this stream foam appears in the main current from time to time. I don't know what causes it but it may be linked to agricultural activities further upstream.

Moved from Insects.

Before this drops off.....
...even though the bugs can't be ID'd, is there anyway to get it saved into the DRAFT: Parasitic Fungi article that Charley Eisemann started?

This image hasn't been frassed, so it's not in immediate danger of disappearing... and I don't see any harm in keeping it here in purgatory until it gets figured out.

Warren, if you can find an individual bug that shows the most detail, maybe you could add an image that's cropped just to that bug, and someone might be able to figure it out based on wing venation etc.

I just added this image to our little gallery of horrors that Nancy linked to above.

Maybe this is stating the obvious,
but in case you hadn't realized, they seem to have a fungus - the white part is different enough on each one to indicate it's not part of their natural appearance. I don't know what they are, though. None of our other fungus-ridden flies have been in water, and in fact judging by the length of the antennae these are not flies at all. Bear in mind this is probably not their natural wing position.

Caddisflies, maybe?

Or alderflies?

Not necessarily frassed!
This image looks fine to me. I wish I had a clue what the insects are! Aphids, perhaps?

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