Gall

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Galls (from the

fungi and bacteria, to other plants, insects and mites
. Plant galls are often highly organized structures so that the cause of the gall can often be determined without the actual agent being identified. This applies particularly to insect and mite plant galls. The study of plant galls is known as cecidology.

Taxonomic range

Plant galls are caused by a wide range of organisms, including animals such as insects, mites, and nematodes; fungi; bacteria; viruses; and other plants.

Insects

Insect galls are the highly distinctive plant structures formed by some herbivorous insects as their own microhabitats. They are plant tissue which is controlled by the 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. Some galls act as "physiologic sinks", concentrating resources in the gall from the surrounding plant parts.[2] Galls may also provide the insect with physical protection from predators.[3][4]

Insect galls are usually induced by chemicals injected by the larvae 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. To form galls, the insects must take advantage of the time when plant cell division occurs quickly: the growing season, usually spring in temperate climates, but which is extended in the tropics.

The meristems, where plant cell division occurs, 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.

scale insects, psyllids, thrips, gall moths, and weevils.[5]

Many gall insects remain to be described. Estimates range up to more than 210,000 species, not counting parasitoids of gall-forming insects.[6]

Cynipid wasps

More than 1400 species of cynipid wasps cause galls. Some 1000 of these are in the tribe Cynipini, their hosts mostly being oak trees and other members of the Fagaceae (the beech tree family).[6] These are often restricted taxonomically to a single host species or a group of related species.

Non-cynipid wasps

Some wasps from other groups, such as the

Chalcidoidea
, also cause plant galls.

Hemipteran bugs

Among the

Adelges abietis, which parasitises coniferous
trees such as the Sitka spruce and the Norway spruce.

Dipteran flies

Some

dipteran flies such as the cecidomyiid gall midges Dasineura investita and Neolasioptera boehmeriae, and some Agromyzidae
leaf-miner flies cause galls.

Mites

Mites, small arachnids, cause distinctive galls in plants such as the

lime tree
.

Nematodes

Nematodes are microscopic worms that live in soil. Some nematodes (Meloidogyne species or root-knot nematodes) cause galls on the roots of susceptible plants. The galls are often small.[7][8]

  • Nematode galls
  • Juvenile Meloidogyne penetrating a host plant
    Juvenile
    Meloidogyne
    penetrating a host plant
  • Root-knot galls caused by the nematode Meloidogyne
    Root-knot galls caused by the nematode
    Meloidogyne

Fungi

Many

Millettia pinnata leaves and fruits. Leaf galls appear like tiny clubs; however, flower galls are globose. Exobasidium
often induces spectacular galls on its hosts.

The fungus Ustilago esculenta associated with Zizania latifolia, a wild rice, produces an edible gall highly valued as a food source in the Zhejiang and Jiangsu provinces of China.[9]

Bacteria and viruses

Gall-causing bacteria include Agrobacterium tumefaciens and Pseudomonas savastanoi.

Gall forming virus was found on rice plants in central Thailand in 1979 and named rice gall dwarf. Symptoms consisted of gall formation along leaf blades and sheaths, dark green discoloration, twisted leaf tips, and reduced numbers of tillers. Some plants died in the glasshouse in the later stages of infection. The causal agent was transmitted by the hemipteran bug Nephotettix nigropictus after an incubation of two weeks. Polyhedral particles of 65 nm diameter in the cytoplasm of phloem cells were always associated with the disease. No serologic relationship was found between this virus and that of rice dwarf.

Plants

The

hemiparasitic plant mistletoe forms woody structures sometimes called galls on its hosts.[10] More complex interactions are possible; the parasitic plant Cassytha filiformis sometimes preferentially feeds on galls induced by the cynipid wasp Belonocnema treatae.[11]

Uses

Galls are rich in

gallnuts
as part of the tanning process as well as a dye-base for ink.

Medieval

intestinal ailments.[13]

See also

References

  1. ^ "gall(4)", Merriam-Webster Online Dictionary, accessed November 16, 2007: "an abnormal outgrowth of plant tissue usually due to insect or mite parasites or fungi and sometimes forming an important source of tannin".
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  12. ^ Bavli, tractate Gittin:19a
  13. . Retrieved 22 June 2020.

Further reading

External links

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