Galls

Galls on plants that are produced by either insects or mites, represent specific yet abnormal plant growths that were induced to be formed by some specific outside organism (i.e. the insect or mite). Those organisms that induce galls can only do so on a narrow range of host material; often within a plant genus and, in some cases, only on a very limited number of plant species. These type of galls represent a very long co-evolution between an insect or mite species and a limited plant group. Usually, gall formation is induced when the insect or mite begins feeding at a critical time in the plant's development or growth. Powerful compounds within the saliva actually alters the genetic message in the individual plant cells and alters the message within the shoot, leaf, or other tissue from developing normally to that of producing the gall. Galls always surround the gall-inducing organism offering protection and a food source. However, there exists a number of parasites that specialize in attacking gall-inhabiting insects.

Galls that are found on foliage and flowers are usually only considered to be an aesthetic curiosity in their importance. However, when galls are formed on the stems and branches of the host plant, death of those parts, and even the entire plant, may occur.

Like leaf miners, gall-inducing insects and mites are extremely difficult to control once gall formation has occurred. Gall formation on individual plants may vary greatly from one year to the next. If the plant is able to grow beyond the point of where gall formation can be introduced then few or no galls will occur. The timing of attack by the pest, therefore, is extremely important to the level of severity.

Galls index:
Cooley Spruce Gall Adelgid
Eastern Spruce Adelgid

Questions about downloading files followed by the symbol? Click here for more info.