Leaf Galls

leaf galls

Insect induced plant galls are abnormal growths of plant cells which form as a response to invasion by the insect - caused by egg-laying or feeding of larvae/nymphs in the plant tissue. Eggs are usually laid in actively growing plant tissue. A chemical stimulant may be injected by the insect to induce a response by the plant or larvae may produce a stimulant when feeding within the plant tissue. Once stimulated, the plant tissue grows around the egg or immature insect and it becomes enclosed by the gall. The immature insect remains sheltered and protected and feeds only on gall tissue during its development.

Gall size and shape is dependant on the species which induced its formation. Galls may be small blisters, round balls or tubes and they may be hairy, smooth or covered with spines. They may occur anywhere on the plant - leaves, branches, stems, petioles etc. More than one type of gall may occur on an individual plant or plant part at one time.

The number of immatures living within each gall is also dependant on species. Immatures may live individually or in groups and a gall may have a number of chambers housing each individual.

Gall forming insects include aphids, psyllids, midges and cynipid wasps (commonly known as gall wasps).