INSECT-INDUCED PLANT GALLS - part 1         
   by Dr. Ros Blanche


   Stem galls on eucalypt
Stem galls on eucalypt
                                                                (Photo ©  Ros Blanche)

The leaves of Australian native plants, especially eucalypts and acacias, are often distorted into curious shapes or have strange-looking lumps on them. Stems or flower buds can also be swollen and malformed. Many people notice these deformations but few realise that these “galls”, as they are called, are usually the result of insect activity. Some insects have the ability to direct plants to provide them with a home. Other organisms, like fungi, nematodes, micro-organisms and mites can also induce galls but the majority are caused by insects.

The inside wall of an insect-induced gall is usually composed of highly nutritious cells. This allows the insect to feed without having to chew through tough plant tissue or hard-to-digest plant chemicals, like oils and tannins. In addition, the gall keeps the insect relatively safe from predators and diseases that would attack the insect if it lived externally.

There are a multitude of questions that can be asked about insect-induced galls on Australian native plants. For example:  How do insects cause a plant to form a gall? How do galls affect their host plants? Which groups of insects cause plant galls? Which life stages, and how many of them, live in a gall? How do gall
-inducing insects mate? How do insects exit the gall? Do gall-inducing insects have any enemies? Do gall inducing-insects cause any problems for people? Do gall-inducing insects or their galls have any uses? The answers to many of these questions are scattered throughout the literature and others still need to be determined.

An illustrated book about Australian insect-induced galls is now available from CSIRO publishing (June 2012). It brings together all the currently known facts about these unusual insects and details some of their remarkable adaptations, relationships and interactions with other organisms and plants - including the negative and positive impacts they can have on human activities.

   Leaf galls on eucalypt

Leaf galls on eucalypt
                                                           (Photo ©  Ros Blanche)
PART ONE               PART TWO
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