Where to look for AFB symptoms
Frame inspection involves visually searching for AFB symptoms on both the surface of capped brood and in the contents of uncapped cells.
Perforated, sunken or discoloured cappings should be investigated by scraping off the cappings with the sharp corner of the hive tool. It is also worth checking capped cells that, judging from the appearance of the surrounding cells, should have emerged i.e. capped cells surrounded by young uncapped brood.
When the cell capping has been removed, or when a suspect uncapped cell is found, the colour and shape of the larvae/pupae should be observed.
Inspect every frame
Every brood frame in the hive should be inspected. Although a thorough inspection like this may take more time, both beekeeper experience and scientific trials have shown that inspecting all the brood frames in a hive pays important dividends, especially when it comes to identifying new, low-level infections before they have a chance to spread (see more on inspecting brood frames).
Every frame of brood should be inspected for AFB.
Check as many cappings as you can
In some cases, beekeepers are confronted with large numbers of cells with chewed cappings that need to be checked for AFB. This is often the case with colonies affected by sacbrood, chalkbrood, Halfmoon Disorder (HMD) or Parasitic Mite Syndrome (PMS). In colonies with these conditions there may sometimes be thousands of chewed cappings.
It is important that a beekeeper does not just uncap a few cells when making an AFB diagnosis. Just because 100 of the cells have been uncapped and a chalkbrood infected larvae has been found underneath each one, this does not mean there is not an AFB infected larvae under one of the other chewed cappings that have yet to be removed.
Beware of AFB - recheck the hive after treating a different condition
In one case when a beekeeper came to take off the honey supers he was faced with an apiary of 20 hives that had PMS because of high varroa numbers. He checked some of the thousands of cells with perforated cappings and correctly diagnosed them as having PMS. He then removed the honey boxes and treated the hives for varroa. The honey supers were extracted and stored with the rest of his supers.
When he removed the varroa treatments six weeks later, the PMS had disappeared and he discovered to his dismay that the colonies also had AFB. He was then faced with the problem that he had 40 honey supers that had come off AFB hives mixed in with all of his other stored supers. Because he could not identify the supers he was forced to put all his supers onto uninfected colonies the following spring and see which developed AFB.
The best way to deal with a hive that has a very large number of cells with perforated cappings, but does not appear to have AFB, is to mark the hive and remove nothing from it. The next step is to eliminate the major cause of the chewed cappings, by requeening (for sacbrood or chalkbrood), or treating the varroa (for PMS). The colony can then be checked for AFB.
If a colony can’t be checked properly because there are too many cells with perforated cappings, mark the hive, remove nothing, clear up the other condition and then inspect the hive.