Visual Indications of EFB
When a high proportion of the larvae are being killed by EFB, the brood pattern will often appear patchy and erratic as dead brood is removed by the bees and the queen lays in the vacant cells.
Bacteria visible in gut
The gut of an infected larva may be visible through its translucent body wall. It has a creamy white colour caused by the mass of bacteria living within it.
The dead larva often collapses, as though melted, turning yellowish-brown and eventually drying up to form a loosely- attached scale.
Where larval remains dry to form scales, these are variable in colour, loose (easily removed) within the cell and somewhat ‘rubbery’, unlike the hard black firmly attached scales of AFB.
European Foul Brood (EFB)
Bacterium: Melissococcus plutonius
European foulbrood is caused by the bacterium Melissococcus plutonius. The bacteria multiply in the mid-gut of an infected larva, competing with the larva for its food. They remain in the gut and do not invade the larval tissue; larvae that die from the disease do so because they have been starved of food. This normally occurs shortly before their cells are due to be sealed.
Unlike AFB, EFB effects larvae before the cell is sealed and can therefore be detected more readily.
EFB mainly affects unsealed brood, killing larvae before they are sealed in their cells. An easy way to remember this is: EFB = E (Early infection before sealing of the cell).
The EFB-infected larva moves inside its cell instead of remaining in the normal coiled position characteristic of a healthy larva of the same age. When it dies, it lies in an unnatural attitude – twisted spirally around the walls, across the mouth of the cell or stretched out lengthways from the mouth to the base.