Photo: Big Bend National Park, salt cedar and giant cane on the Rio Grande. © 2017 Delena Norris-Tull
Biological Controls: Their use in managing invasive plants in Western States
Summaries of the research and commentary prepared by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, September 2020. Note: I am not an expert on biocontrol agents. But I attempt here to summarize the research from various experts, on the effectiveness, limitations, and impacts of biocontrol agents.
Biological controls include the use of invertebrates (including insects, mites, midges, nematodes, and spiders), livestock (such as sheep, goats, or cattle), fish, birds, or pathogens (including viruses, bacteria, and fungi) to control the spread of either pests in crops or noxious weeds in crops or in natural landscapes.
Insects are the main biological control agents used to manage noxious weeds, with a few mites, midges, fungi, and nematodes also in use. Viruses, bacteria, and fungi are mainly used to control insect pests, as alternatives to chemical pesticides. Mites, midges, nematodes, and spiders are also used primarily to control insect pests.
A few researchers have found a few nematodes, primarily gall-forming nematodes, that can be used to control noxious weeds (Parker, 1991). Little research has as yet been conducted on this use of nematodes.
Useful resources on biocontrol
Refer to the website, ibiocontrol.org for details on the many biocontrol agents in use throughout the world. That important website points out that it takes years for the success or failure of a biocontrol agent to be accurately documented. Thus, any research cited here should be evaluated with that caveat in mind. However, I would caution that it also takes years to ascertain whether or not a particular biocontrol agent has any detrimental impacts on the environment into which it is introduced, including its potential impacts on related native species. As with so many other aspects of the management of invasive species, we simply do not have enough research on this aspect of management.
Also refer to the blog on biocontrol agents in the Western USA, hosted on the Centre for Agriculture and Bioscience International (CABI) website.
A recent book on the topic is Biological Control: Ecology and Applications, by Heimpel and Mills, 2017. And with the caveat that this resource is now more than two decades old, refer to the book, Biological Control of Weeds in the West by Rees, et al., 1996, part of which is available online.
A brief history of the use of biocontrol agents
“Exotic weeds in natural and managed ecosystems have long been targeted, starting with the cases of prickly pear (Opuntia sp.) in India (1863), then Sri Lanka (1865), and Australia (1912), and lantana (Lantana camara) in Hawai’i in 1902” (Suckling & Sforza, 2014).
The 1945 Western Weed Control Conference is the first regional US conference at which biocontrol insects are mentioned (refer to the archival minutes of that meeting). Mr. Ball reported on research being conducted in cooperation with the US Bureau of Entomology and Plant Quarantine on two biological control insects. These insects had been effective in use in Australia. He stated, “These insects have been brought into California, after thoroughly investigating the possibilities of their detriment to other plants or crops. A complete series of starvation tests have been carried out to prove that they would not be destructive to other plants. They attack nothing but Hypericum (goatweed). We do not know anything as yet about the natural predators, which may prey upon these insects. If they are present, our hopes for control will be very limited.”
At the 1946 Western Weed Conference, in the California report given by Walter S. Ball, he stated: “… We have always looked on Klamath weed, or St. John’s wort, as one of our major weed problems and it is still a major project in California. It has caused such heavy losses to our stockmen, through depletion of the ranges, that it is worthy of attention and we will continue to discuss it as long as it is of importance.
“The most recent important phase of this program is the work being started on the biological control of Klamath weed. A beetle which belongs to the Chrysomelid group feeds upon the Hypericum species in Australia and in some instances has actually killed out heavily infested areas.
“The entomologist of the Experiment Station, of the College of Agriculture, working with the Federal quarantine officials as well as the State officials, has taken all the precautionary steps in introducing this insect to California in the hope that it might find favorable conditions where it will breed and increase, and at the same time assist in the control of this weed. Starvation tests were carried out at the Experiment Station in Berkeley to further assure workers the beetle would not injure other crops; that it favors and will live only on Hypericum species. Releases of the insects have been made in three or four areas in the State under slightly different ecological conditions. In one of those areas, located in Marin County, the insect has fed upon the plant and is starting to increase in numbers. This is the first encouraging report we have had. This work is in a purely experimental stage and we feel it may be years before the population is increased to a point where it will reach economic importance.”
Julien and Griffiths, 1998, developed a catalogue listing all biocontrol agents in use worldwide on noxious weeds. Their lists include invertebrates, fungi, and fish. “In the 20th century, 1,120 releases of 365 species of biological control agents were made against 133 weeds in 75 countries, predominately USA, Canada, Australia, South Africa and New Zealand” (Suckling & Sforza, 2014).
Suckling and Sforza, 2014, conducted an extensive review of the literature on biocontrol use and its ecological impacts on native plant species. Through their review, Suckling and Sforza contacted experts in the field and located data on an additional 147 agents, beyond those documented by Julien and Griffiths, 1998. That brings the total to 512 agents released for biocontrol worldwide, as of 2012. The additional 147 agents include 129 insects, 5 mites, 12 pathogens, and one nematode.
Suckling and Sforza, 2014, found that the annual cost savings in the US from the use of biocontrol agents exceeded $180 million U.S. dollars, much of which results from the subsequent reduction in the use of herbicides. Similar cost savings have been found in various other countries.
“Classical biological control of weeds involves the deliberate introduction of exotic organisms, or biological control agents, to manage weed problems in the invaded range. It offers an excellent and sustainable solution for invasive species” (Suckling & Sforza, January, 2014).
References:
Links to information on Biocontrol Agents:
Biological Controls: Their use in managing invasive plants in Western States
Summaries of the research and commentary prepared by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, September 2020. Note: I am not an expert on biocontrol agents. But I attempt here to summarize the research from various experts, on the effectiveness, limitations, and impacts of biocontrol agents.
Biological controls include the use of invertebrates (including insects, mites, midges, nematodes, and spiders), livestock (such as sheep, goats, or cattle), fish, birds, or pathogens (including viruses, bacteria, and fungi) to control the spread of either pests in crops or noxious weeds in crops or in natural landscapes.
Insects are the main biological control agents used to manage noxious weeds, with a few mites, midges, fungi, and nematodes also in use. Viruses, bacteria, and fungi are mainly used to control insect pests, as alternatives to chemical pesticides. Mites, midges, nematodes, and spiders are also used primarily to control insect pests.
A few researchers have found a few nematodes, primarily gall-forming nematodes, that can be used to control noxious weeds (Parker, 1991). Little research has as yet been conducted on this use of nematodes.
Useful resources on biocontrol
Refer to the website, ibiocontrol.org for details on the many biocontrol agents in use throughout the world. That important website points out that it takes years for the success or failure of a biocontrol agent to be accurately documented. Thus, any research cited here should be evaluated with that caveat in mind. However, I would caution that it also takes years to ascertain whether or not a particular biocontrol agent has any detrimental impacts on the environment into which it is introduced, including its potential impacts on related native species. As with so many other aspects of the management of invasive species, we simply do not have enough research on this aspect of management.
Also refer to the blog on biocontrol agents in the Western USA, hosted on the Centre for Agriculture and Bioscience International (CABI) website.
A recent book on the topic is Biological Control: Ecology and Applications, by Heimpel and Mills, 2017. And with the caveat that this resource is now more than two decades old, refer to the book, Biological Control of Weeds in the West by Rees, et al., 1996, part of which is available online.
A brief history of the use of biocontrol agents
“Exotic weeds in natural and managed ecosystems have long been targeted, starting with the cases of prickly pear (Opuntia sp.) in India (1863), then Sri Lanka (1865), and Australia (1912), and lantana (Lantana camara) in Hawai’i in 1902” (Suckling & Sforza, 2014).
The 1945 Western Weed Control Conference is the first regional US conference at which biocontrol insects are mentioned (refer to the archival minutes of that meeting). Mr. Ball reported on research being conducted in cooperation with the US Bureau of Entomology and Plant Quarantine on two biological control insects. These insects had been effective in use in Australia. He stated, “These insects have been brought into California, after thoroughly investigating the possibilities of their detriment to other plants or crops. A complete series of starvation tests have been carried out to prove that they would not be destructive to other plants. They attack nothing but Hypericum (goatweed). We do not know anything as yet about the natural predators, which may prey upon these insects. If they are present, our hopes for control will be very limited.”
At the 1946 Western Weed Conference, in the California report given by Walter S. Ball, he stated: “… We have always looked on Klamath weed, or St. John’s wort, as one of our major weed problems and it is still a major project in California. It has caused such heavy losses to our stockmen, through depletion of the ranges, that it is worthy of attention and we will continue to discuss it as long as it is of importance.
“The most recent important phase of this program is the work being started on the biological control of Klamath weed. A beetle which belongs to the Chrysomelid group feeds upon the Hypericum species in Australia and in some instances has actually killed out heavily infested areas.
“The entomologist of the Experiment Station, of the College of Agriculture, working with the Federal quarantine officials as well as the State officials, has taken all the precautionary steps in introducing this insect to California in the hope that it might find favorable conditions where it will breed and increase, and at the same time assist in the control of this weed. Starvation tests were carried out at the Experiment Station in Berkeley to further assure workers the beetle would not injure other crops; that it favors and will live only on Hypericum species. Releases of the insects have been made in three or four areas in the State under slightly different ecological conditions. In one of those areas, located in Marin County, the insect has fed upon the plant and is starting to increase in numbers. This is the first encouraging report we have had. This work is in a purely experimental stage and we feel it may be years before the population is increased to a point where it will reach economic importance.”
Julien and Griffiths, 1998, developed a catalogue listing all biocontrol agents in use worldwide on noxious weeds. Their lists include invertebrates, fungi, and fish. “In the 20th century, 1,120 releases of 365 species of biological control agents were made against 133 weeds in 75 countries, predominately USA, Canada, Australia, South Africa and New Zealand” (Suckling & Sforza, 2014).
Suckling and Sforza, 2014, conducted an extensive review of the literature on biocontrol use and its ecological impacts on native plant species. Through their review, Suckling and Sforza contacted experts in the field and located data on an additional 147 agents, beyond those documented by Julien and Griffiths, 1998. That brings the total to 512 agents released for biocontrol worldwide, as of 2012. The additional 147 agents include 129 insects, 5 mites, 12 pathogens, and one nematode.
Suckling and Sforza, 2014, found that the annual cost savings in the US from the use of biocontrol agents exceeded $180 million U.S. dollars, much of which results from the subsequent reduction in the use of herbicides. Similar cost savings have been found in various other countries.
“Classical biological control of weeds involves the deliberate introduction of exotic organisms, or biological control agents, to manage weed problems in the invaded range. It offers an excellent and sustainable solution for invasive species” (Suckling & Sforza, January, 2014).
References:
- Heimpel, G.E, & Mills, N.J. (2017). Biological Control: Ecology and Applications. Cambridge: Cambridge University Press.
- Julien, M.H., & Griffiths, M.W. (1998). Biological control of weeds: A world catalogue of agents and their target weeds. Wallingford, U.K.: CAB International.
- Parker, P.E. (1991). Nematodes as biological control agents of weeds. In D.O. TeBeest (Ed.), Biological Control of Weeds. London: Routledge, Chapman, & Hall.
- Rees, N.E., Quimby, Jr., P.C., Piper, G.L., Coombs, E.M, Turner, C.E., Spencer, N.R., & Knutson, L.V. (Eds.) (1996). Biological Control of Weeds in the West. Western Society of Weed Science.
- Suckling, D.M., & Sforza, R.F.H. (January, 2014). What magnitude are observed non-target impacts from weed biocontrol? PLoS ONE 9(1). Doi:10.1371/journal.pone.0084847
Links to information on Biocontrol Agents: