Colour of brood

Healthy versus unhealthy larvae colour

Healthy larvae and freshly capped pupae are pearly white in colour (Fig. 15).

Infected larvae and pupae change from pearly white to a brown colour resembling coffee with milk (Fig.16). The distinctive coffee-brown colour is often considered a definitive symptom of AFB, although brownish-coloured larvae can sometimes be found that have died from causes other than AFB.

 

Figure 13: Healthy prepupa

Figure 16: Coffee coloured AFB


There is also a significant variation in the colour of AFB infected larvae and pupae, ranging from very pale brown to almost black. The variation depends on the progression of the disease and the degree of drying of the diseased material. After about a month, the infected larvae or pupae will dry out completely and turn totally black (Fig. 17). Dried out, infected larvae and pupae are commonly referred to as “scale”.
  Figure 17: Pupal scale with tongue

 

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