What is biological control?

Biological control is the deliberate use of one organism to regulate the population size of a pest organism. There are three main branches of biological control.

Classical biological control is the control of pests introduced from another region through importing specialized natural enemies of the pest from its native range. The aim is to establish a sustained population of the natural enemies.
Conservation biological control aims to manipulate the environment to favor natural enemies of the pest. Pedro Barbosa (University of Maryland) has written and excellent book on the topic.
Augmentation biological control occurs when the number of biolotical control agents is supplemented. Inoculation is the introduction of a small number of individuals of the biological control agent, while inundation is the introduction of vast numbers of individuals. This over all approach is common when the biological control agent can not survive the entire year, or can not achieve densities high enough to regulate the pest population.

The pros and cons of biological control.
The benefits of biological control are that it can provide fairly permanant regulation of devastating agricultural and environmental pests that may be difficult or impossible to manage with more traditional chemical means. However, there are obvious risks. Biological control agents may negatively affect native species directly or indirectly. Historically biological control introductions were not regulated the way they are today, and some horrible mistakes were made in the name of biological control (e.g. cane toads in Australia). Even relatively specialized herbivorous insects released for the biological control of invasive weeds can pose risk to related native plants.

The risks inherent to biological control have led to a strong backlash against it. Where once it was touted as the "environmentally safe" way to control pests without toxic chemicals, it is now reviled as being a cure worse than the disease. I feel that neither polemical perspective has merit. Biological control is both powerful and risky. With caution and study, safe, effective biological control should be possible. We simply need to take the time necessary to do the appropriate research prior to considering an introduction, and to weigh the pros and cons very carefully.

Given past mistakes, and the complexity of envionmental interactions, it is quite difficult to predict the outcome of a biological control introduction. I believe that introductions should only be made of organisms that are both host specific and likely to be effective.

Here are a couple additional links on biological control:
Biological Control - NYSAES guide to natural enemies
Biological Control Virtual Information Center

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