Something incredible happened at Tempe Reserve over the summer. Lots of Acacia trees came to the end of their life with limbs falling or trunks breaking. Most have been removed leaving a visual hole behind, which the weeds are rapidly filling. There are not many Acacia trees left, but some of those remaining become hotels for galls.
I have been told these galls are caused by Rust Fungus, which can kill the tree. I’ve never seen so many galls in one place.
A gall is a lump of bump or in this case a whole structure that forms on leaves, stems or buds of plants. Some of the galls at Tempe Reserve are as big as a small grapefruit, while most range between a lemon & an orange in size.
The galls hang from the trees like decorations. Originally they were a fresh terracotta colour, but have turned dark brown & hardened as they have aged.
Galls can be formed as a result of bacteria, viruses, fungi or physical damage. They are a response by the plant or tree in response to attack.
Insects such as thrips, wasps, midges, beetles & moths also induce the formation of galls. How this happens, no-one knows exactly, but it is thought to be a result of the saliva of the larva growing inside the gall or as a result of the insect laying the eggs. The host tree or plant responds by reorganizing the cells to develop an abnormal growth.
Galls provide food, shelter & safety for their inhabitants who emerge when evolved from a grub to a mature insect. I read that Eucalypts & Acacias are the trees most prone to develop galls in Australia.