Plant Galls

Page 1

TRANSACTIONS PLANT GALLS DR. G .

D.

HEATHCOTE

ALL animals are dependent upon plants in one way or another, but the animal-plant relationship is particularly close and complex in what we call 'galls'—structures produced specifically by plants in the presence of an animal (usually an insect, but sometimes a mite, an eelworm, or some other small creature). Some fungi and bacteria can also induce gall formation. Galls are seldom studied by the amateur naturalist, partly because we take them for granted ('marble galls' of oak are almost as common as acorns) but largely because the small creatures that cause them are difficult to identify. One other discouraging factor is the complex nature of the Community of insects that can be found in a single gall. Not only is the original gall-former present, but insects that parasitise it, or insects that simply use the gall as a home ('inquilines'). There may also be insects that parasitise the parasites ('hyperparasites'). Truly, 'greater fleas have little fleas upon their backs to bite 'em, little fleas have lesser fleas, and so ad infinitum!' The 'Robin's pincushion' galls on wild rose provide an excellent example of the 'complex' within a gall. These 'hairy' red growths, an inch or more across, are common in Suffolk. They are also known by the unusual name of 'bedeguars' (apparently from the Persian Ianguage). In each gall are several Chambers, with a single larva of a gall wasp (Rhodites rosae) in each. The galls also may contain certain inquiline gall wasps (Periclistus brandtii), or parasites (Orthopelma luteolator or Torymus bedeguaris) that attack the original inhabitants or the inquilines. A hyperparasite (Habrocytus bedeguaris) may be present, or other parasitic wasps (chalcids). About sixty per cent of all types of gall in Britain are found on oak, representing the homes of some 500 species of insects, and of fifty-four species of Cynipids alone. Recently I found three types of galls on oak within flve minutes at the roadside near Barton Mills. The best known oak galls are probably the hard brown marble galls previously mentioned. These contain the larvae of a gall wasp (Cynips kollari), one in each gall. Marble galls were unknown in Britain until about 1830, but then spread rapidly. They contain seventeen per cent tanic acid and were probably introduced for use in dyeing cloth. Cynips can reproduce without males ('parthenogenesis'). Virgin birth is also found in greenfly and some other insects.


Turn static files into dynamic content formats.

Create a flipbook
Issuu converts static files into: digital portfolios, online yearbooks, online catalogs, digital photo albums and more. Sign up and create your flipbook.