Galls or plant galls are abnormal outgrowths of plant tissues and can be caused by various parasites, from fungi and bacteria, to insects and mites. Galls are often very organised structures and because of this, cause of the gall can often be determined without the actual agent being identified. This applies particularly to some insect and mite galls.
Causes of plant galls
develop under the influence of gall-inducing insects
. Insect galls are usually induced by the chemicals injected by the larvae
or the adults
in the plants, either including mechanical damage or not. After the galls are formed, the larvae develop inside until fully grown, at which time they leave, sometimes as adults. In order to form galls, the insects must seize the time when plant cell division occurs at a high speed, the growing season, usually spring in temperate climates, but which can be extended in tropical latitudes. Also, the specific places where plant cell division occurs are needed to induce galls, that is, the meristems
. Although insect galls can be found on a variety of parts of the plant, such as the leaves, stalks
or even flowers
, gall-inducing insects are usually species-specific and sometimes tissue-specific on the plants they gall. Some insects induce galls on plants similar to each other, frequently within genera or family.
Gall-inducing insects include gall wasps, gall midges, gall flies, aphids, and psyllids.
A gall-inducing fungus is: Cedar-apple rustGalls
are often seen in Pongamia pinnata leaves and fruits. Leaf galls appear like tiny clubs, however, flower galls are globose.(Suma TS, FRLHT, Bangalore)
Bacteria and viruses
is an example of a gall-causing bacterium.
can form galls on its hosts
Galls are rich in resins and tannic acid and have been used in the manufacture of permanent inks (such as iron gall ink) and astringent ointments, in dyeing, and in tanning. A high-quality ink has long been made from the Aleppo gall, found on oaks in the Middle East; it is one of a number of galls resembling nuts and called "gallnuts" or "nutgalls'. The larvae in galls is useful for a survival food and fishing bait.