Editing Biological pest control (section)

==Difficulties==
Many of the most important pests are exotic, invasive species that severely impact agriculture, horticulture, forestry, and urban environments. They tend to arrive without their co-evolved
parasites, pathogens and predators, and by escaping from these, populations may soar. Importing the natural enemies of these pests may seem a logical move but this may have [[unintended consequences]]; regulations may be ineffective and there may be unanticipated effects on biodiversity, and the adoption of the techniques may prove challenging because of a lack of knowledge among farmers and growers.<ref>{{cite journal|author1=Messing, Russell H. |author2=Wright, Mark G.  |year=2006 |title=Biological control of invasive species: solution or pollution? |journal=Frontiers in Ecology and the Environment |volume=4 |issue=3 |pages=132–140 |doi= 10.1890/1540-9295(2006)004[0132:bcoiss]2.0.co;2|url=https://www.researchgate.net/publication/233794457 |url-status=live |archive-url=https://web.archive.org/web/20170410051543/https://www.researchgate.net/profile/Mark_Wright6/publication/233794457_Biological_control_of_invasive_species_Solution_or_pollution/links/00b7d52cdb2f1a2810000000.pdf |archive-date=2017-04-10 }}</ref>

===Side effects===

Biological control can affect [[biodiversity]]<ref name=follett/> through predation, parasitism, pathogenicity, competition, or other attacks on non-target species.<ref name=council>{{cite book|last=National Research Council |date=1996 |title=Ecologically Based Pest Management:New Solutions for a New Century |publisher=The National Academies Press |url=https://www.nap.edu/read/5135/chapter/1 |url-status=live |archive-url=https://web.archive.org/web/20160725125103/http://www.nap.edu/read/5135/chapter/1 |archive-date=2016-07-25 |doi=10.17226/5135 |isbn=978-0-309-05330-3 }}</ref> An introduced control does not always target only the intended pest species; it can also target native species.<ref>{{cite web |publisher=Society for Conservation Biology |date=2002 |title=Biocontrol backfires again |url=http://www.scienceblog.com/community/older/2002/C/20025043.html |access-date=31 July 2009 |url-status=dead |archive-url=https://web.archive.org/web/20110716014858/http://www.scienceblog.com/community/older/2002/C/20025043.html |archive-date=16 July 2011 }}</ref> In Hawaii during the 1940s parasitic wasps were introduced to control a lepidopteran pest and the wasps are still found there today. This may have a negative impact on the native ecosystem; however, host range and impacts need to be studied before declaring their impact on the environment.<ref name=wright>{{cite journal | last1=Wright | first1=M. G. | last2=Hoffmann | first2=M. P. | last3=Kuhar | first3=T. P. | last4=Gardner | first4=J | last5=Pitcher | first5=SA | year=2005 | title=Evaluating risks of biological control introductions: A probabilistic risk-assessment approach | journal=Biological Control | volume=35 | issue=3| pages=338–347 | doi=10.1016/j.biocontrol.2005.02.002| bibcode=2005BiolC..35..338W }}</ref>

[[File:Cane toad distribution stills.png|thumb|[[Cane toad]] (introduced into Australia 1935) spread from 1940 to 1980: it was ineffective as a control agent. Its distribution has continued to widen since 1980.]]

Vertebrate animals tend to be generalist feeders, and seldom make good biological control agents; many of the classic cases of "biocontrol gone awry" involve vertebrates. For example, the [[cane toad]] (''Rhinella marina'') was intentionally introduced to [[Australia]] to control the [[cane beetle|greyback cane beetle]] (''Dermolepida albohirtum''),<ref>{{Cite web |title=Cane Toad |url=http://www.nt.gov.au/nreta/wildlife/animals/canetoads/index.html |website=Exotic Animals – Major Pests |publisher=Northern Territory Government, Australia |access-date=14 March 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110315083841/http://www.nt.gov.au/nreta/wildlife/animals/canetoads/index.html |archive-date=15 March 2011 }}</ref> and other pests of sugar cane. 102 toads were obtained from [[Hawaii]] and bred in captivity to increase their numbers until they were released into the sugar cane fields of the tropic north in 1935. It was later discovered that the toads could not jump very high and so were unable to eat the cane beetles which stayed on the upper stalks of the cane plants. However, the toad thrived by feeding on other insects and soon spread very rapidly; it took over native [[amphibian]] [[habitat]] and brought foreign disease to native [[toad]]s and [[frog]]s, dramatically reducing their populations. Also, when it is threatened or handled, the cane toad releases [[poison]] from [[parotoid gland]]s on its shoulders; native Australian species such as [[goanna]]s, [[tiger snake]]s, [[dingo]]s and [[northern quoll]]s that attempted to eat the toad were harmed or killed. However, there has been some recent evidence that native predators are adapting, both physiologically and through changing their behaviour, so in the long run, their populations may recover.<ref>{{cite web|url=https://www.environment.gov.au/biodiversity/invasive-species/publications/factsheet-cane-toad-bufo-marinus |title=The cane toad (''Bufo marinus'') |year=2010 |publisher=Australian Government: Department of the Environment |access-date=2 July 2016 |url-status=live |archive-url=https://web.archive.org/web/20160712233540/http://www.environment.gov.au/biodiversity/invasive-species/publications/factsheet-cane-toad-bufo-marinus |archive-date=12 July 2016 }}</ref>

''[[Rhinocyllus conicus]]'', a seed-feeding weevil, was introduced to North America to control exotic [[Carduus nutans|musk thistle]] (''Carduus nutans'') and [[Cirsium arvense|Canadian thistle]] (''Cirsium arvense''). However, the weevil also attacks native thistles, harming such species as the [[Endemism|endemic]] [[Cirsium neomexicanum|Platte thistle]] (''Cirsium neomexicanum'') by selecting larger plants (which reduced the gene pool), reducing seed production and ultimately threatening the species' survival.<ref>{{cite journal |author1=Rose, K. E. |author2=Louda, S. M. |author3=Rees, M. |year=2005 |title=Demographic and evolutionary impacts of native and invasive insect herbivores: a case study with Platte thistle, ''Cirsium canescens'' |journal=Ecology |volume=86 |issue=2 |pages=453–465 |doi=10.1890/03-0697 |url= http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1061&context=bioscifacpub }}</ref> Similarly, the weevil ''[[Larinus planus]]'' was also used to try to control the [[Cirsium arvense|Canadian thistle]], but it damaged other thistles as well.<ref>{{cite book |title=Operational Field Guide to the Propagation and Establishment of the Bioagent Larinus Planus |date=May 2001 |publisher=Province of British Columbia, Ministry of Forests |url=https://www.for.gov.bc.ca/hra/plants/downloads/FieldGuide_Larinus_planus.pdf |access-date=2019-01-30 |archive-url=https://web.archive.org/web/20181113204115/https://www.for.gov.bc.ca/hra/plants/downloads/FieldGuide_Larinus_planus.pdf |archive-date=2018-11-13 |url-status=dead }}</ref><ref name=Louda>{{cite journal |last1=Louda |first1=Svaa M. |last2=O'Brien |first2=Charles W. |title=Unexpected Ecological Effects of Distributing the Exotic Weevil, Larinus planus (F.), for the Biological Control of Canada Thistle |journal=Conservation Biology |date=June 2002 |volume=16 |issue=3 |pages=717–727 |doi=10.1046/j.1523-1739.2002.00541.x |bibcode=2002ConBi..16..717L |s2cid=2367835 |url= http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1027&context=bioscilouda}}</ref> This included one species classified as threatened.<ref>{{cite journal |last1=Havens |first1=Kayri |author-link=Kayri Havens |last2=Jolls |first2=Claudia L. |last3=Marik |first3=Julie E. |last4=Vitt |first4=Pati |last5=McEachern |first5=A. Kathryn |last6=Kind |first6=Darcy |date=October 2012 |title=Effects of a non-native biocontrol weevil, Larinus planus, and other emerging threats on populations of the federally threatened Pitcher's thistle, Cirsium pitcheri |journal=Biological Conservation |volume=155 |pages=202–211 |doi=10.1016/j.biocon.2012.06.010|bibcode=2012BCons.155..202H }}</ref>

The [[small Asian mongoose]] (''Herpestus javanicus'') was introduced to [[Hawaii]] in order to control the [[rat]] population. However, the mongoose was diurnal, and the rats emerged at night; the mongoose, therefore, preyed on the [[endemic birds of Hawaii]], especially their [[egg]]s, more often than it ate the rats, and now both rats and mongooses threaten the birds. This introduction was undertaken without understanding the consequences of such an action. No regulations existed at the time, and more careful evaluation should prevent such releases now.<ref>{{cite web|url=http://mauiinvasive.org/2012/04/18/moving-on-from-the-mongoose-the-succuss-of-biological-control-in-hawaii/ |title=Moving on from the mongoose: the success of biological control in Hawai'i |date=18 April 2012 |website=Kia'i Moku |publisher=MISC |access-date=2 July 2016 |url-status=live |archive-url=https://web.archive.org/web/20160619021310/http://mauiinvasive.org/2012/04/18/moving-on-from-the-mongoose-the-succuss-of-biological-control-in-hawaii/ |archive-date=19 June 2016 }}</ref>

The sturdy and prolific [[eastern mosquitofish]] (''Gambusia holbrooki'') is a native of the southeastern United States and was introduced around the world in the 1930s and '40s to feed on mosquito larvae and thus combat [[malaria]]. However, it has thrived at the expense of local species, causing a decline of endemic fish and frogs through competition for food resources, as well as through eating their eggs and larvae.<ref>{{Cite book|author=National Research Council (U.S.). Board on Agriculture and Natural Resources |title=Incorporating science, economics, and sociology in developing sanitary and phytosanitary standards in international trade: proceedings of a conference |url=https://books.google.com/books?id=KsQuyCgumREC&pg=PA97 |access-date=12 August 2011 |date=June 2000 |publisher=National Academies Press |isbn=978-0-309-07090-4 |page=97 |url-status=live |archive-url=https://web.archive.org/web/20130611162144/http://books.google.com/books?id=KsQuyCgumREC&pg=PA97 |archive-date=11 June 2013 }}</ref> In Australia, control of the mosquitofish is the subject of discussion; in 1989 researchers A. H. Arthington and L. L. Lloyd stated that "biological population control is well beyond present capabilities".<ref>{{cite web|url=http://www.gambusia.net/ |title=Gambusia Control |access-date=2 July 2016 |url-status=live |archive-url=https://web.archive.org/web/20160716125052/http://www.gambusia.net/ |archive-date=16 July 2016 }}</ref>

===Grower education===
A potential obstacle to the adoption of biological pest control measures is that growers may prefer to stay with the familiar use of pesticides. However, pesticides have undesired effects, including the development of resistance among pests, and the destruction of natural enemies; these may in turn enable outbreaks of pests of other species than the ones originally targeted, and on crops at a distance from those treated with pesticides.<!--<ref>{{cite book |author=Thacker, J.R.M. |date=2002 |title=An Introduction to Arthropod Pest Control |publisher=Cambridge University Press }}</ref>--><ref>{{cite web |last1=Charlet |first1=Larry |title=The Impact of Pesticides on Natural Enemies |url=http://www.entomology.wisc.edu/mbcn/fea202.html |publisher=University of Wisconsin Department of Entomology |access-date=9 April 2017 |url-status=dead |archive-url=https://web.archive.org/web/20141014222138/http://www.entomology.wisc.edu/mbcn/fea202.html |archive-date=14 October 2014 }}</ref> One method of increasing grower adoption of biocontrol methods involves letting them learn by doing, for example showing them simple field experiments, enabling them to observe the live predation of pests, or demonstrations of parasitised pests. In the Philippines, early-season sprays against leaf folder caterpillars were common practice, but growers were asked to follow a 'rule of thumb' of not spraying against leaf folders for the first 30 days after transplanting; participation in this resulted in a reduction of insecticide use by 1/3 and a change in grower perception of insecticide use.<ref>{{cite journal | last1=Heong | first1=K. L. | last2=Escalada | first2=M. M. | year=1998 | title =Changing rice farmers' pest management practices through participation in a small-scale experiment | journal=International Journal of Pest Management | volume=44 | issue=4 |  pages=191–197 | doi=10.1080/096708798228095}}</ref>