Hi Nelson, I think that 's a good question for discussion.

In my oppinion, I believe that it is necessary to know a lot more about this field. We need go out and see what is happening in the ecosystems. Probably, with the time, some herbivory insect (New natural enemies on non-native range) could be adapted to alien plant species and they can changing their ecological behavior in the presence of this invasive plant. In last months, I saw some interesting things about this fact. On the other hand, I believe that using exotic natural enemies or probably modified, could be a serious problem.

There are many examples of biological control which turned to be disasters for the ecosystems (e.g. introduction of the mollusc Euglandina rosea to fight with invasive Achatina fulica), did not bring an effect (control of rabbits in Australia by introduce virus) and few that worked out (Chrysolina quadrigemina used in N. America to stop invasive Hypericums sp. or  Cactoblastus cactorum to stop Opuntia in Australia). The main problem with biological control is that we don't know species biology properly and that species evolve. Thus, even if we are almost sure that they are monophagus and will control only invader, it may turn after some years or decades that they are detrimental also for some native species. The best would be to have at hand some kind of control over the species used for biological control ... but this is impossible. So far success stories are mainly about monophagous insects developing on one species of plant. In my opinion biological control is tricky and chances for success are much smaller than chances for failure.

Good number of case studies prove this an effective approach, but before such approach EIA needs to be done.

Good points everyone. Applied biological control is an important component in Integrated Pest Management programs. Hoddle 2004 provides a great overview on this topic. Biological control has changed dramatically over the last 100 years. In the US, exotic biocontrol agents have to undergo extensive safety testing and get federal apporval  before they are released in the field. They are often specialists that only attack the target pest.

http://biocontrol.ucr.edu/hoddle/ccbcdisk_g00002b.pdf

Thanks Erica. That is a very good paper on the issue, it gives a summary of the history and possible prospects of biological control procedures. However, as he points out, are these control agents feasible (economically and ecologically) over a long period of time? The biological control agent should in theory consume massive amounts of the invader so as to render its populations non-self sustaining.  Take an example of Water hyacinth (Eichhornia crassipes) in most water bodies of Africa and its re-invasion of L. Victoria. Can the weevils consume this water weed to the point of total removal from a water body? Or will there be a point in time when the biological control agent develops a sort of "plant-herbivore interaction" equilibrium. Moreover, a rapid deterioration of plant quantity and quality can lead to an early decline in weevil populations.

I am very skeptical of any attempts at biocontrol. Even with rigorous testing, we are unable to know enough about the ecological systems involved to fully predict risk. I realize completely that we need to control and/or eliminate invasive plants and animals. I prefer that we try to learn as much about the system so that we can try to use fire and other management processes before attempting biocontrol. In many cases I am even more favorable of herbicides as long as the testing is rigorous.

An old and well cited case is the alien parasitic moth controlling an invasive alien Opuntia in South Africa; this represents the only case of near total control among the many invasive alien plants known in Southern Africa. However, here in neighbouring Namibia the cactus is spreading relentlessly. Obviously, effective biocontrol, or other control, of invasive aliens is rare.

A test case of Chromolaena control is shortly described in the attached; although optimism prevailed a decade ago, success seems still illusive.

Elimination of invasive plants seems treating the symptoms to me; the disease, if any, is the rapid and widespread creation of open habitats and access for dispersal agents. Treatment of the disease could mean avoiding the creation of open ground and canopies, re-vegetating open habitats with indigenous plants and dispersal (e.g. access) control.

Article Efficacy of Chromolaena odorata control in a South African c...

After prevention and early detection and eradication of incipient populations has failed, control is your last and least satisfying option when invasive plants are widespread. Control usually involves reducing impacts at important sites using chemical or manual control methods, for example on farms where the impacts are unacceptable or where there are high biodiversity values. Costs are usually too prohibitive to control the invader wherever it occurs. Biocontrol is the next option and has the potential to reduce the fitness (spread rate or growth rate) wherever the plant occurs. Modern biocontrol research involves extensive testing with coevolved invertebrate browsers or predadors (and sometimes diseases). Success rates in terms of achieving control and no unpredicted unacceptable non-target effects have been very high in the last 20-40 years.  The modern methods e.g. "centrifugal" testing involves testing for non-target effects using  many closely related taxa and fewer more distantly related species. This kind of introduction pales in comparison to the many unintentional introductions of plant pests and diseases that results from international trade, and has the potential to reduce important invader's impacts. An abundance of caution is warranted but I strongly disagree with the general thrust of   assessments of Applegate and Jaroszewicz. Dozens and dozens of agents have contributed controlling effects in multiple jurisdictions. The lessons from other locations can be applied to control where the invasive flora share taxa that already have had research into biocontrol and had good results. It is true that complete control would rarely if ever be achieved using any biocontrol but great improvements can be had in terms of mitigating impacts. One review of success rates from nearly two decades ago for one country that has implemented a lot of programs: Fowler et al Success and safety in the biological control of environmental weeds in New Zealand Austral Ecology 25 553-562

Suckling, D. M., & Sforza, R. F. H. (2014). What magnitude are observed non-target impacts from weed biocontrol?. PloS one, 9(1), e84847 say that " Our analysis shows (as far as is known), weed biological control agents have a biosafety track record of >99% of cases avoiding significant non-target impacts on plant populations."

Clewley, Gary D., et al. "The effectiveness of classical biological control of invasive plants." Journal of Applied Ecology 49.6 (2012): 1287-1295.

Paynter Q, Fowler SV, Gourlay AH, Peterson PG, Smith LA, Winks CJ. 2015. Relative performance on test and target plants in laboratory tests predicts the risk of non-target attack in the field for arthropod weed biocontrol agents. Biological Control 80(0): 133–142. DOI: 10.1016/j.biocontrol.2014.10.007.

I am also very skeptical. The examples of biological control which went wrong are too numerous to take the risks for the ecosystems. Manual control methods are often the best choice. 

I agree with Juliette,

methods as mulching and removing biomass are more safety and without any risks. The best way is to find some possibility to use such plants/animals for feeding, heating, preparing biologicaly active agents....then alien could be changed to crop. Good luck!

Dear everyone. I am very skeptical of any attempt at biological control. As we read before there are some examples or wrong results with disastrous consequences. Having said that I think that some improvement and control of possible native enemies in the invaded range may be effective to some extent. Of course, we need continuously monitor and a complete study about the new relationship. Study to understand and understand to act.

It is critical that the biological control agents introduced to control invasive alien plants into a country do not become pests themselves. Considerable testing is done prior to the release of biological control agents to ensure they will not pose a threat to non-target species such as native and agricultural plants. Although in the long term, biological control can be cost effective and can reduce the need for less desirable management practices, not all weeds are suitable for biological control. Developing a biological control project requires a substantial investment, sometimes costing millions of dollars over many years. In Australia for instance  the first step is to undertake host specificity testing. This is a requirement under the Australian Government Department of Agriculture - Biosecurity  to ensure that the agent will not damage native flora or agricultural stock or crops. Once host specificity testing is completed, biological control agents must be assessed to meet the requirements of the Quarantine Act 1908 and the Environment Protection and Biodiversity Conservation Act 1999 (the EPBC Act) before approval can be given for their introduction and reléase.

Note there was the European Parasite Laboratory of the USDA, first in Versailles, later in Behoust (both in France) and now all bibliography produced there (namely on biocontrol of weeds and other invasive species by natural enemies) is in the library of CNRS associated to the Montpellier University (France). The former Director of the European Parasite Laboratory was David B. Perkins, now retired for a while and living (?) near S. Francisco. During long years he did a huge work in this domain and though "ancient" literature is considered old fashioned, there is lots of very serious and valid information there. It really is a pity that since Internet functioning, much of the existing data from solid research are lost if not scanned. It seems to me that many research is done again as if it had never been done before. Looking for David Perkins I know that his son is working at the American Embassy in Madrid (Spain). Another source for weed control informations from all over the World is the Publications from the annual Ghent (Belgium) Meetings on Plant Protection, where Prof. Hull and his numerous students published regularly (don't remember exactly wether it was during 25, 30 or even 40 years).  It was not my subject of research, but I accompanied several times D. Perkins to places in Portugal where weeds were endemic and he screened for natural enemies, before starting all that testing at Behoust . Don't know wether these ideas might be supplementary to your other search tools.

Here is an example of a very successful biocontrol project that worked as planned and controlled a highly invasive Acacia species in South Africa, without causing collateral damage on indigenous species:

http://www.invasive.org/proceedings/pdfs/11_574-575.pdf

The point is that biocontrol can be effective and does not have to create problems. It comes down to conducting good research on the cross-infectivity of the potential biocontrol pest or disease on a wide range of potential host species that are indigenous.

In the long term, it is the only viable solution, to provide for a systems balance in an ecologically sound, and balanced system.

The bad examples are all cases where there was poor research, and poor strategic planning on the question: how could this go wrong ?

Classical approach of biological weed control rely on the purchase of insects for the control of weeds from that country only from which a particular exotic alien weed species came into role...Another approach is bioherbicidal technical know-how based on applying biologically synthesized herbicide to the weed species to get rid of that problem from the field...There are many more mycohervicides which are specific to weeds and crops...like devine is for dorangle vine in citrus, Collego for joint vetch in rice, Bipolaris for jhonshan grass, Biomal for malvae species etc