What is Biocontrol?
Biological Control or biocontrol is the use of an invasive plant's natural enemies - agents (chiefly insects, parasites and pathogens) - to reduce its population below a desired level. It is the long-term, self-sustaining treatment method for managing invasive plants, and can be divided into two approaches:
The FLNRO Invasive Plant Program uses the classical biocontrol approach to bring invasive plant species to an acceptable socio-economic and ecological level.
Under classical biological control an invasive plant will never be eradicated since the bioagent's population will decline after the invasive plant population has been reduced. As one's population increases or decreases, the other's will follow due to the increased or diminished supply of food, or conversely, feeding pressure.
Classical biocontrol agents may kill the invasive plants directly or indirectly
by decreasing reproductive and competitive abilities or plant vigour, which in turn encourages
the re-establishment of native vegetation.
Invasive plants result in economic losses and costs to control the invasive plants themselves in order to mitigate further economic losses. To date there are no compiled estimates of these costs in BC. However:
Biocontrol is a long-term solution for management of invasive plants. Over time, other treatment methods become increasingly unnecessary, and may
eventually not be needed at all. It is desirable to decrease the amount of herbicide applied to the environment (or potentially applied in the future) and to decrease economic losses and costs for control.
Radtke, H. 1993. An Economic Evaluation of Biological Control of Tansy Ragwort. Oregon Dept. of Agric. State Weed Board, Oregon, U.S.A.
Each biocontrol agent attacks its host plant in a specific manner. The visible symptoms of attack may be damaged leaves, flowers, stems or roots and/or wilting, discoloration, dropping of leaves, reduced numbers and viability of seeds, and retarded growth or flowering periods.
Biological control agents can generally be described in the following categories:Gall Producing Insects: Gall producing insects produce atypical growths on plants through either larval feeding or female oviposition. The resulting gall (enlargement) causes the plant to direct nutrients into the gall tissue, rather than into seeds or plant growth. For different species, galls can be located on different plant tissues, for example, on roots versus stems or seed heads.
Defoliators: Defoliators partially, or completely, consume or mine leaves and associated stem tissue. This loss of nutrition reduces the plant's ability to produce sugars for the root system, thus suppressing growth and survival.
Sap Suckers: Insects and mites with piercing-sucking mouthparts feed on nutrients in the plant's circulatory system, weakening the plant. Viruses, bacteria and fungi that are pathogenic and specific to the plant can also be transmitted during these attacks.
Flower and Seed Feeders: Flower and seed feeders affect reproductive tissues such as flower tissue or some or all of the seeds by consuming tissue and/or nutrients intended for seed production. Seed viability is then greatly reduced.
Stem Miners: During larval development, insects mine within the plant's tissues. Plant pathogens carried by the miners can cause secondary damage once the stem miner leaves its hosts. Feeding activity by insects in the plant's stem reduces nutrient reserves and can impair the plant's ability to translocate nutrients.
Crown Feeders: Feeding activity by insects in the plant's crown reduces nutrient reserves and can impair the plant's ability to translocate nutrients. Pathogens can cause secondary damage here as well.
Root Feeders: These insects bore into the roots or feed on root hairs and young roots, reducing nutrient reserves and the plant's ability to acquire and translocate moisture and nutrients. Soil pathogens may also enter the roots through the wounds.
Parasites: An organism that lives on or in another organism, or at the expense of another organism but does not kill its host.
Pathogens: Any-disease-producing microorganism. Principal pathogens include bacteria, viruses, fungi and nematodes.
Gordh, G. and D.H. Headrick. 2001. A Dictionary of Entomology. CABI Publishing, Oxon, UK
Delegates and participants to the X International Symposium for Biological Control of Weeds, recognizing the need for professional standards in the subdiscipline of classical biological control of weeds, urge practitioners of the subdiscipline to voluntarily adopt the CODE OF BEST PRACTICES FOR CLASSICAL BIOLOGICAL CONTROL OF WEEDS, as published in the proceedings of the Symposium, and to adhere to the principles outlined in the Code.
For additional information about the Code and each guideline, consult the chapter "International Code of Best Practices for Classical Biological Control of Weeds" by Balciunas and Coombs, pp. 130- 136 in the handbook "Biological Control of Invasive Plants in the United States" (Coombs, et al., 2004. Oregon State Univ. Press, Corvallis.
The use of biocontrol in British Columbia involves a retrospective set of actions, separated into stages that can be thought of as the Biocontrol Cycle.
"Healthy, functioning BC ecosystems, free of the impacts of invasive plants."