Galls (Cecidia) are outgrowths on the surface of plants. Plant galls are abnormal outgrowths of plant tissues and can be caused by various parasites, from fungi and bacteria to insects and mites. Plant galls are often highly organized structures and because of this, the cause of the gall can often be determined without the actual agent being identified. This applies, particularly to some insect and mite plant galls.
Insect galls act as both the habitat and food source for the maker of the gall. The interior of a gall can contain edible nutritious starch and other tissues. Galls may also provide the insect with physical protection from predators. They are usually induced by chemicals injected by the larvae or the adults of the insects into the plants, and possibly mechanical damage. After the galls are formed, the larvae develop inside until fully grown, when they leave. In order to form galls, the insects must seize the time when plant cell division occurs quickly. For example, the growing season is usually during spring in temperate climates. The meristems are the tissue in most plants which contain undifferentiated cells. It’s the zones where plant cell division occurs. These areas are the usual sites of galls, though insect galls can be found on other parts of the plant, such as the leaves, stalks, branches, buds, roots, and even flowers and fruits. Gall-inducing insects are usually species-specific and sometimes tissue-specific on the plants they gall.
Gall-inducing insects include gall mites, gall wasps, gall midges, gall flies, aphids and psyllids.
Fungi galls: Rustcan also induces the formation of galls and can be seen on leaves as tiny clubs or as flowers gall which is globose.
Bacteria & Virus can also cause gall formation.
Other plants: Mistletoe can form galls on its hosts
Nematodes: Root-knot nematodes are one of the most economically damaging genera of plant-parasitic which attacks many vegetables and fruits.
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