Microscopic diagnosis

Ascosphaera apis has septate hyphae (2.5–8.0 µm in diameter) which show pronounced dichotomous branching (Spiltoir, 1955; Skou, 1988). As mentioned above, this is a heterothallic fungus with two mating types and only when + and - strains are grown in close proximity does the formation of fruiting bodies occur. The fruiting bodies are spherical spore cysts (47–140 µm in diameter; Fig. 3a) which contain numerous spore balls (9-19 µm, Fig. 3b) composed of hyaline spores (2.7–3.5 x 1.4–1.8 µm, Fig. 3c) (Skou, 1972; Bissett, 1988).

Fig. 3. Scanning electron microscope pictures of Ascosphaera apis fruiting body. A. Spherical fruiting body; B. Cracked fruiting body with sporeballs; C. Sporeballs with multiple ascospores. Photos: J Bresciani and A B Jensen.

Figure 3