Indirect Control

Indirect management measures result in delayed mortality to the pest population. There are various methods that have been employed, including genetic manipulation, quarantines, and biological control methods.

Genetics

Genetic Improvement

Often, a portion of a population is less affected by a pest than is the remainder of the population. This ability to tolerate attack by a pest may result from inherent resistance in the population. When resistance is genetically based, favoring and propagating resistant individuals will add a measure of protection to the next generation. Breeding to enhance genetic resistance takes advantage of a natural process, augmenting it but not significantly altering it. However, as managers breed genetically resistant plants, pest populations adapt to attack the newly developed resistant host material. The process of genetic manipulation is, therefore, an ongoing process, not a permanent solution.

In recent years a new technology, genetic engineering (which involves altering the genetic structure of living organisms at the molecular level), has emerged. Pests can be engineered, altering their genes to make them less successful in reproducing or less aggressive in attacking potential host material. Alternatively, hosts can be genetically engineered to make them more resistant, or even toxic, to invading pests. Currently, little genetic engineering is being done with southern forest trees. The potential of this method is unclear because use of this method is currently very controversial. Genetic engineering is perceived by some as having the potential to accidentally kill beneficial organisms or even to create new pests.

Quarantine

State and Federal agencies often restrict the movement of live plants or animals across State or National boundaries unless they are declared free of pests. These quarantines have been fairly effective in reducing the spread of known pest organisms but have failed to stop many organisms that are not pests in their native environment but become pests when moved. As discussed elsewhere, quarantine restrictions have been ineffective in preventing the introduction of ornamental plants, which subsequently are shown to have no natural enemies in their new ecosystems. Plant quarantine to ensure the health of incoming vegetative materials and prevent the dissemination of infested or infected materials is a critical process for protecting the future health of the southern forests.

Biological Control

Biological control involves the use of one organism to moderate or control the behavior of another organism. In biological control, the manager attempts to locate a natural enemy of a pest and augment its population to control unacceptable population levels of the pest. Viruses, bacteria, fungi, and insects have all been used in biological control (Stairs 1971). Apparent biocontrol of an epidemic population of gypsy moth by the fungus Entomophaga miamiaga, the use of a virus against sawflies, and the use of another fungus against the introduced pine sawfly are examples of successful biocontrol. Biological control, however, suffers from a problem very similar to genetic control. Often, this process has only provided short-term solutions. Natural enemies of a pest organism may fail to colonize the same niche as the pest, and either totally fail as biocontrol agents, or themselves become pests in a niche, they do colonize.