North American Invasive Species Management Association (NAISMA) provides biocontrol resources and supports biological control as an integral part of an Integrated Pest Management (IPM) program. Biological control practitioners from across North America provide technical advice, guidance, and training on IPM, specifically targeting biological control of invasive weeds.
There are many definitions attributed to biological control. For our purposes, we will define the biological control of weeds as the use of live natural enemies (e.g. insects, pathogens, nematodes, mites) of pests to reduce pest population levels below that which would occur in the absence of their natural enemies. There are commonly three types of biological control recognized:
Initially small numbers of natural enemies are released in target pest areas for long-term control.
Large numbers of natural enemies are released to control a target pest for a short amount of time.
Changing environmental conditions to aid in natural enemy survival.
For over 100 years, biological control has been used around the world as an effective, affordable, and environmentally responsible way to reduce the harm caused by invasive species. This method uses natural enemies—like insects, fungi, or other organisms—to help manage invasive plants and animals. It tends to work best on invasive species that are already well established, rather than on newly introduced ones.
The success of biological control can vary. In some cases, it works extremely well and replaces the need for other weed control methods. In others, it may not work at all. Most efforts fall somewhere in between. When biological control doesn’t fully solve the problem, it’s best to use it as part of an Integrated Weed Management (IWM) approach—a strategy that combines multiple tools and techniques to control invasive species more effectively.
Biological control fits well with ecological principles, since it often involves reuniting an invasive species with a natural enemy that helped control it in its original habitat. Ecological science also helps experts predict how well a biological control agent might work and assess any potential risks. By breaking down complex ecological processes into clear, trackable steps, we can better understand what’s working, what isn’t, and how to improve future efforts. This flexible, adaptive approach helps make biological control safer and more effective over time.
When biological control works well, the biocontrol agents—such as insects or fungi—multiply and help reduce the population of the target weed. As the weed becomes less common, the biocontrol agents may also decline, either because they run out of food or move on to other areas with more of the weed.
In many cases, this leads to a natural cycle: the weed population goes up, then the biocontrol agent increases in response, which brings the weed population back down. Over time, both the weed and the biocontrol agent usually settle into a more balanced, lower level.
However, biological control doesn’t work in every situation or at every site. That’s why it’s important to build an Integrated Weed Management (IWM) program that uses a combination of tools—including biological control, where appropriate—to manage invasive weeds more effectively.