Biological control Frequently Asked Questions

Q: What is the rationale behind biological control of non-native, invasive plants?

Invasive plants become successful in new environments because they have been separated from their natural enemies (e.g., herbivores) that feed on them in their countries of origin. Biological control helps restore the normal balance between the invasive plants and their host-specific natural enemies by re-uniting them in their new environment.

Q: What is the goal of successful biological control?

The goal of biological control is to reduce the population growth and spread of an invasive plant, minimizing its impact on invaded ecosystems. The invasive plant will not be eradicated; however, its suppression can allow native plant communities and ecosystems to better compete and recover.

Q: Are there any examples of successful weed biological control programs in Canada?

Yes. Biological control has a long history in Canada starting with successful biocontrol agents for St. John’s Wort in 1952. Recent successes include biocontrol agents for Dalmatian toadflax, houndstongue, leafy spurge and knapweeds. In Ontario, populations of purple loosestrife (Lythrum salicaria) have been successfully managed in large part through the introduction of two species of Galerucella beetles in the mid-1990s.

Q: Will the biological control agents feed on non-target plants?

No. Modern biological control agents undergo intensive testing to assess their host specificity and confirm that they will only develop on the target weed prior to permit approvals. Potential biocontrol agents are exposed to a wide range of taxonomically similar plants in addition to plants of broad economic or cultural significance (e.g., crops). Biological control agents for introduced Phragmites have been tested over 11 years on 45 key representative test-plant species and have been found to be highly specific to Phragmites.

Q: Will the biological control agents evolve to feed on other plants or grow out of control?

No. The biological control agents have evolved over millennia to only feed on introduced Phragmites, as has been demonstrated with host-range testing. There is no ecological basis that makes the agents more or less likely than any other native or non-native species in North America to undergo a rapid change in feeding behaviour. Populations of the agents will be regulated by a variety of mechanisms that affect all species including food supply, competition with themselves, competition with other species, climatic constraints on their habitat range, and predation.

Q: Do the biological control agents represent a risk to native Phragmites?

No. Host-range testing indicates a strong preference for laying eggs on introduced rather than native Phragmites and very poor survival of any eggs that are laid on the native subspecies. Native Phragmites stems are generally too thin to support the life cycle of the moths and the native plant sheds its leaf sheaths during the winter, exposing and killing any eggs laid there. Introduced Phragmites is currently a primary threat to the survival of native Phragmites stands.

Q: Why have some historical releases of biocontrol agents resulted in problems (e.g., cane toads, ladybird beetles)?

These examples were historical releases targeting invasive insects that occurred prior to establishment of strict regulations for the release of biological control agents. They would not occur today. There was no safety testing to screen for non-target impacts prior to their release and the organisms released were generalist predators that consumed a wide range of targets. In contrast, all biological control agents in Canada today (including those for introduced Phragmites) are rigorously tested and confirmed to only attack their target, and only host-specific biological control agents that meet the regulatory and safety requirements of the Canadian Food Inspection Agency (CFIA) are released.

Q: Can biological control be used in conjunction with herbicide treatments?

Yes. Both approaches are important parts of an integrated pest management (IPM) program. Biological control is extremely species-specific and cost-effective at the province-wide scale of the invasion requiring treatment. Biological control agents can be used in close proximity to water and once established do not require repeated treatments because the insects move and find new weed infestations. Careful timing of herbicide or cultural control around the life cycle of the agents can enhance IPM.

Q: How is risk managed when implementing a biological control program?

All management techniques for invasive weeds have some risk to habitats. Decisions regarding release of biological control agents are based on a risk-benefit framework and detailed host-specificity testing to ensure safety. In the case of serious invasive species like Phragmites, the greatest risk to habitats and species comes from doing nothing and allowing them to spread.