Something is eating my seedlings from inside

[mmcavall]

I noticed that many of my cacti seedlings are empty. The epidermis is there, transparent, apparently intact, but there is nothing inside it.
What can cause that?

Can it be any physiological disorder? Or it is caused by any pest?

I see small flies around, but they appear to be more interested in the substrate than in the plants.

I've already applied an acaricide/insecticide, anyway.

I would appreciate any help. Thanks

[ElieEstephane]

I can't remember the exact name but there is a kind of fly larvae that does that

[stefan m.]

which Is why keep my seedlings covered, and spray them with hydrogen peroxide.

[Ivan C]

which Is why keep my seedlings covered, and spray them with hydrogen peroxide.

In my experience when seedlings go white or translucent, they have had too much moisture. Not much can be done since the others like that moisture.

Spray them with hydrogen peroxide will defiantly get rid of the algae but make sure there is not a lot of organic matter. That combination cause a lot of bubbling.

[stefan m.]

Mostly its anti fungal, covering them with 0.3 mm fine sand does the bug fungus gnat protection.
Never had them bloat, just dry out, and eaten by fungus.

[mmcavall]

Thanks all for replying. The seedlings have experienced an excess of humidity due to a deep watering followed by a week of rainy days. I suspect the humid atmosphere contributed to the problem. I let the seed trays dries a little in a more ventilated place, while sprayed the insecticide. Hope it works.