Government of British Columbia Home
Forests, Lands & Natural Resource Operations
Invasive Plant Program

Priorities for New Biocontrol Agents

All the invasive plants addressed to date in the MFLNRO's Biocontrol Development Program are intruders to North America, mostly from Europe and Asia. These invasive plants are prioritized in their need for requiring new biological control agents. During this prioritization process, multiple factors are considered, for example, what makes a particular plant species aggressive and what are the resource values that it affects?

There are several theories why these alien plants are so aggressive on our provincial lands. Two such theories by Callaway and Aschehoug were presented at the 2001 International Knapweed Symposium in Coeur d'Alene, Idaho. The first theory addressed that most of these alien plants, such as knapweed, originated from Eurasia. The land within the many countries this encompasses has been subject to hundreds of years of disturbance. It may be speculated that these invasive plants have evolved to require disturbance. In comparison, land in North America has been subjected to little and recent disturbance. The native vegetation, therefore, has evolved with little disturbance. When we disturb land in North America, these invasive plants may be more adapt to colonize it. The second theory presented was that the co-evolution of plants in Eurasia with the species of concern may have bred resistance to their various competition techniques, whereas in North America, our native vegetation is not resistant to these plants and their invasion.

Additional speculations involve the fact that most invasive plants tend to be polyploids, having a variety of DNA to adapt to many conditions and are, therefore, more aggressive than other species. Also, many invasive plants are prolific seed producers. For example, if one begins with no plants but 100 knapweed seeds, taking into account seed production rates (1000 seeds/knapweed plant) germination rates and seed longevity, in ten years, there would be 4,771,469,407 plants and 5,190,972,273,123 seeds in the seed bank, covering an area of 159,049 hectares if the plants were at a density of 3 plants/square meter. However, the most widely attributed answer to why these alien plants are so aggressive is the fact that most of these plants have arrived in North America without their natural predators and, therefore, may be healthier and more robust than native vegetation fed on by a host of indigenous predators.

It is this last theory that creates the impetus to undertake biological control in BC.Before one pursues finding a biological control agent, the point of accepting that a particular invasive plant is now beyond eradication or control with the other conventional methods has to be reached. Once this has occurred, the next step is to rank the plants within the province in priority of requiring biological control. This is due to the fact that the development of a biological control agent for a particular invasive plant is very slow and expensive. The ranking process must be science based and take into account various factors such as the DNA and the seed producing ability of the plant as mentioned above as well as the environmental and economic factors the infestations affect.

To date this ranking process has been carried out by field specialists in the provincial government. The process is to be formalized and utilized for provincial ranking of invasive alien plants by the Inter Ministry Invasive Plant Working Group (IMIPWG, formerly the IMIPC). This process is intended to be complete and shared publicly at this location in the winter of 2009.


Callaway, R.M. and E. T. Aschehoug. No date. Mechanisms for the success of invaders: diffuse knapweed interacts differently with new neighbours that with old ones. Univ. of Montana, Missoula, The Nature Conservancy, San Francisco.

"Healthy, functioning BC ecosystems, free of the impacts of invasive plants."