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When I try to rear flies from larvae, pupae or leaf mines, it sometimes happens that a newly emerged fly fails to unfold one or both of its wings. Does anyone know what causes this anomaly? Or, even better, how this can be prevented?
Cheers, Louis

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Dear Louis,

There are two reasons that I can think of. First, the atmosphere in the rearing container is too dry, so that the wings are drying too quickly for the newly emerged fly to expand them. The second, that may be more likely, is that the fly emerging from the pupa could not get out of the pupa quickly enough to expand the wings before they dried. If the pupa is loose in the container and when the fly tries to emerge from the pupa it cannot get rid of the pupa until it finds a hold somewhere. When that takes too long, the wings are too dry to expand them. I do not think it is a developmental abarretion as such, but an artefact of rearing.

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Thanks! So it might help to provide extra support for the emerging fly, e.g. put a strip of paper in the glass vial with the pupa.

I think I have also occasionaly seen flies 'in the wild' with only one unfolded wing, but I'm not sure.

Louis