Fassifern Field Naturalists: When is an apple, not an apple?

Sunday, 19 July 2020

When is an apple, not an apple?

Apple galls

On our latest field trip, we came across these funny looking growths on the fresh eucalypt regrowth along the burnt ridge of the Mt Mathieson track. Questions were asked and other than that they were galls made by small insects nothing else was offered.

Recently I've been reading some of our old newsletters and the words of one of our contributors came to me - “…the impulse to know, to want to learn, to discover for one’s self, .... in other words one gets caught up in the excitement of discovery.” This was me in a box. I wanted to know more about these galls.

Searching the www finds a little information though usually quite academic but I was hooked. I was caught up in the excitement of discovery.

More apple galls

The type of gall depends on the parasite that produces it. They can be wasps, beetles, midges or something even smaller such as viruses, fungi and bacteria. The insect parasite lays her egg in the plant which forms a protective, woody growth around it. Hence a gall. Psyllids, tiny sap-sucking insects related to lerps, cause galls on native trees. Schedotrioza spp. form distinctive spherical “apple” galls on eucalypt leaves.

Psyllids are approximately 4 mm long and hold their wings roof-like over their bodies and look a little like miniature cicadas. The immature psyllids are specialist feeders, with many species restricted to one plant type or even a single species of plant, and often to particular parts of the plant (leaves, new shoots, etc.) or growth stages (either young or mature foliage). Adults disperse over short distances by jumping or flying, but many species may travel long distances on air currents.