ECOLOGY

Galls & fungi

There are many gall forming insects that attack acacias. These insects are often specific to either the flower buds, foliage or stems. They may also be specific to a host Acacia species or groups of species. Gall formers include wasps, mites and thrips, and the latter may also inhabit the phyllode nectaries.eThe gall-midge (Cecidomyidae) produces a salivary substance (cecidotoxin)(Matthews 1976) which stimulates the plant to produce the gall cells in which the gall-midge live. These primary gall-formers suck the cell contents, but they in turn may be parasitised by other insects, such as moth larva, wasps, weevils and beetles.

All parts of the plant may be subject to fungal attack, and some Acacia species appear to be more prone to this than others. The sugary secretions from the phyllode gland may also assist in the formation of black sooty moulds on the phyllodes and branchlets. Besides being formed by insects, galls may also be formed by some fungi, such as by the Uromycladium sp. fungus. This infestation, which may cause large brown galls, often observed on Acacia implexa trees, can be severe, and at times, debilitate the plant. The insects which may be associated with these galls, for example the beetle Eriemodes australis: Cucujoidea (Lawrence & Britton 1994) and moth lava (Walsh & Entwisle 1996) are not the cause of the malformation.

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