Photo: Kochia, southwest Montana. © 2020 Delena Norris-Tull
Insects as Biocontrol Agents
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020.
“After some assessment of cost-benefit ratio, the process involves collecting exotic natural enemies to control a target invasive weed, usually followed by importing, rearing, testing, and release from quarantine for establishment. Host specificity tests are conducted in artificial and field conditions, and increasingly combined with ecological and molecular evaluations” (Suckling & Sforza, January, 2014).
Louda, et al., 1997, reported that, in the US, 41% of biocontrol projects, using insects from the plant’s native range, have had some success in reducing populations of the target weed, and 20% of projects have shown significant control of the target weed species. However, that means that 39% had been unsuccessful. A significant number of advances have been made in the use of biocontrols since 1997, as described below.
More recently, Sheley, et al., 2011, conducted an extensive review of the research on the long-term effectiveness of biological control agents on rangeland ecoystems. They concluded that, with the exception of a few highly effective agents, overall, biological control agents have not proven effective for large-scale infestations over the long-term. And “the risks of deleterious off-target effects increase with the number of releases.” The few documented successes include two beetles that have been highly effective with reducing infestations of St. John’s wort, and three insects used on ragwort. They also found some success with the Diorhabda species used on salt cedar (see concerns about these species, described under “Indirect effects”). The advantage of biological control agents is that they are relatively inexpensive, when compared with herbicides (which are often unsuccessful). They found that a number of studies demonstrated that native species do successfully re-emerge, after reduction of invasive species via biological control agents, although not all studies had this result.
Sheley, et al., 2011, found that, “When operating under current protocols there are relatively few documented direct effects… on desirable vegetation… There is, however, mounting evidence suggesting that poor monitoring efforts, difficulty in predicting biocontrol effects, and the largely unrecognized indirect effects biocontrols can have on ecosystems contributes to an underestimation of the detrimental effects…on desirable vegetation… For example, the bulk of biocontrol monitoring focuses on release sites with little attention paid to offsite biocontrol effects even though there is strong evidence demonstrating landscape-scale variation in biocontrol effects on desirable vegetation… In addition, it is estimated that less than half of the biological control efforts… in the United States demonstrated any evidence of control…. [In addition] recent literature [shows] complex indirect effects of biocontrol on desirable vegetation. For example, following the collapse of the target [invasive] population, intense competition among biocontrol agents can cause a transient increase in host [invasive] plant range, which results in the biocontrol agents attacking desirable species… When biocontrol agents only moderately damage invasion plants they may increase invasive plant…compensatory growth… Current procedures do not adequately prevent biocontrol efforts from having significant effects on desirable vegetation.” Other research indicates that biocontrol insects can have negative direct or indirect impacts on native insects and other animals, such as mice, within the food chain.
References:
Next Sections on Insects as Biocontrol Agents:
Additional reports on Biocontrol Agents:
Insects as Biocontrol Agents
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020.
“After some assessment of cost-benefit ratio, the process involves collecting exotic natural enemies to control a target invasive weed, usually followed by importing, rearing, testing, and release from quarantine for establishment. Host specificity tests are conducted in artificial and field conditions, and increasingly combined with ecological and molecular evaluations” (Suckling & Sforza, January, 2014).
Louda, et al., 1997, reported that, in the US, 41% of biocontrol projects, using insects from the plant’s native range, have had some success in reducing populations of the target weed, and 20% of projects have shown significant control of the target weed species. However, that means that 39% had been unsuccessful. A significant number of advances have been made in the use of biocontrols since 1997, as described below.
More recently, Sheley, et al., 2011, conducted an extensive review of the research on the long-term effectiveness of biological control agents on rangeland ecoystems. They concluded that, with the exception of a few highly effective agents, overall, biological control agents have not proven effective for large-scale infestations over the long-term. And “the risks of deleterious off-target effects increase with the number of releases.” The few documented successes include two beetles that have been highly effective with reducing infestations of St. John’s wort, and three insects used on ragwort. They also found some success with the Diorhabda species used on salt cedar (see concerns about these species, described under “Indirect effects”). The advantage of biological control agents is that they are relatively inexpensive, when compared with herbicides (which are often unsuccessful). They found that a number of studies demonstrated that native species do successfully re-emerge, after reduction of invasive species via biological control agents, although not all studies had this result.
Sheley, et al., 2011, found that, “When operating under current protocols there are relatively few documented direct effects… on desirable vegetation… There is, however, mounting evidence suggesting that poor monitoring efforts, difficulty in predicting biocontrol effects, and the largely unrecognized indirect effects biocontrols can have on ecosystems contributes to an underestimation of the detrimental effects…on desirable vegetation… For example, the bulk of biocontrol monitoring focuses on release sites with little attention paid to offsite biocontrol effects even though there is strong evidence demonstrating landscape-scale variation in biocontrol effects on desirable vegetation… In addition, it is estimated that less than half of the biological control efforts… in the United States demonstrated any evidence of control…. [In addition] recent literature [shows] complex indirect effects of biocontrol on desirable vegetation. For example, following the collapse of the target [invasive] population, intense competition among biocontrol agents can cause a transient increase in host [invasive] plant range, which results in the biocontrol agents attacking desirable species… When biocontrol agents only moderately damage invasion plants they may increase invasive plant…compensatory growth… Current procedures do not adequately prevent biocontrol efforts from having significant effects on desirable vegetation.” Other research indicates that biocontrol insects can have negative direct or indirect impacts on native insects and other animals, such as mice, within the food chain.
References:
- Louda, S.M., Kendall, D., Connor, J., & Simberloff, D. (22 August, 1997). Ecological effects of an insect introduced for biological control of weeds. Science 277 (5329), 1088-1090.
- Sheley, R.L., James, J.J., Rinella, M. J., Blumenthal, D., & DiTomaso, J.M. (2011). Invasive plant management on anticipated conservation benefits: A scientific assessment. In D.D. Briske (Ed.) Conservation benefits of rangeland practices: Assessment, recommendation, and knowledge gaps. (pp. 293-336). USDA Natural Resources Conservation Service.
- 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
Next Sections on Insects as Biocontrol Agents:
Additional reports on Biocontrol Agents: