How does the fungus Septobasidium interact with scale insects?

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Two Amanita pantherina mushrooms with brown caps covered in white spots grow among moss and fallen leaves. — fungus A pair of panther cap mushrooms (*Amanita pantherina*). Closely related to the death cap mushroom (*Amanita phalloides*), the panther cap is highly poisonous.

The fungal genus Septobasidium maintains a specialized, complex parasitic relationship with scale insects that feed on tree bark. The fungus grows elaborate structures over insect colonies, where it extends haustoria into the bodies of some insects to feed on them without causing their death.1

While the parasitized insects are rendered sterile, the fungus provides a protective cover for the rest of the colony against predators. This relationship facilitates a mutual survival strategy: newly hatched insects crawl over the sporulating fungus, picking up spores that they carry to new feeding sites, thereby establishing new fungal colonies. In this ecological arrangement, the insect acts as a parasite on the tree, while the fungus acts as a parasite on the insect, ultimately making the tree the primary victim of the interaction.1