Appearance of the infection
At first, diseased larvae or pre-pupae are slightly yellow in colour. As decomposition advances they become coffee-coloured and extend lengthwise in the cells.
On stirring with a match or similar probe, the contents of the cell may rope out forming a fine elastic thread up to 30 mm long.
In the advanced stages, the brood pattern has a pepperbox appearance. On drying out, the diseased larvae or pre-pupae become dark brown and form a scale along the lower cell wall. Good lighting is required to observe these scales, as they are similar in colour to dark brood combs.
Cappings, if present, will be either perforated or if the disease is well established, most of them will be sunken with a water-soaked appearance.
Where death has occurred during pupation, a partly developed tongue may protrude as a fine thread upwards and backwards from the scale. Under Queensland conditions, this symptom is rare.