What could be causing this?

[megadyptes]

Walking near the hive this morning I noticed some debris on the ground outside the entrance, and what looks to be a load of wax fragment underneath the OMF. The debris looks (to my novice eyes) to be the husks of bees that don't appear to have successfully made it to adulthood, but I could be wrong.

When inspecting the hive on the weekend, I noticed a handful (~5) uncapped cells that contained white adult-looking proto-bees, and a couple of cells that looked plugged with a cotton-wool like substance.

Not sure if there's a link, or it's purely coincident, but this weekend was also when i loaded the first Apiguard tray into the hive. Could this have triggered something?

Is this chalk brood, if so what can be done about it, or is it something else?

 

[masterBK]

Thymol based products do lead to the loss of some brood as bees move away from the brood. Exposed larvae are also more likely to get chalk brood so Apiguard is the cause but it is only a temporay problem and the benefits of getting Varroa numbers down more thna compensates.