Editing Biological pest control

{{short description|Controlling pests using other organisms}}
{{redirect|Biocontrol|the journal on this subject|BioControl}}
{{good article}}
[[File:Syrphid.maggot3554.5.13.08cw.jpg|thumb|250px| ''[[Syrphus]]'' hoverfly larva (below) feed on [[Aphididae|aphids]] (above), making them natural biological control agents.]]
[[File:Cotesia9061.8.15.07.c.jpg|thumb|250px| A [[parasitoid wasp]] (''[[Cotesia congregata]]'') adult with pupal cocoons on its host, a tobacco hornworm (''[[Manduca sexta]]'', green background), an example of a [[hymenoptera]]n biological control agent]]

'''Biological control''' or '''biocontrol''' is a method of [[pest control|controlling pests]], whether pest animals such as [[insect]]s and [[mite]]s, [[weed]]s, or [[pathogens]] affecting animals or [[phytopathology|plants]] by [[bioeffector|using other organisms]].<ref>{{cite book |author=Flint, Maria Louise |author2=Dreistadt, Steve H. |editor=Clark, Jack K. |title=Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control |publisher=University of California Press |year=1998 |isbn=978-0-520-21801-7 |url=https://books.google.com/books?id=FBJvpMqcV9UC |url-status=live |archive-url=https://web.archive.org/web/20160515072525/https://books.google.com/books?id=FBJvpMqcV9UC |archive-date=15 May 2016}}</ref> It relies on [[predation]], [[parasitism]], [[herbivory]], or other natural mechanisms, but typically also involves an active human management role. It can be an important component of [[integrated pest management]] (IPM) programs.

There are three basic strategies for biological control: classical (importation), where a natural enemy of a pest is introduced in the hope of achieving control; inductive (augmentation), in which a large population of natural enemies are administered for quick pest control; and inoculative (conservation), in which measures are taken to maintain natural enemies through regular reestablishment.<ref>{{Cite web |url=http://jenny.tfrec.wsu.edu/opm/displaySpecies.php?pn=-40 |title=Biological control |last=Unruh |first=Tom R. |date=1993 |website=Orchard Pest Management Online, Washington State University |access-date=8 November 2017 |archive-url=https://web.archive.org/web/20181206205201/http://jenny.tfrec.wsu.edu/opm/displaySpecies.php?pn=-40 |archive-date=6 December 2018 |url-status=dead }}</ref>

Natural enemies of insects play an important part in limiting the densities of potential pests. Biological control agents such as these include [[Predation|predators]], [[parasitoid]]s, [[pathogen]]s, and [[Competition (biology)|competitors]]. Biological control agents of plant diseases are most often referred to as antagonists. Biological control agents of weeds include seed predators, [[herbivore]]s, and plant pathogens.

Biological control can have side-effects on [[biodiversity]] through attacks on non-target species by any of the above mechanisms, especially when a species is introduced without a thorough understanding of the possible consequences.

==History==

The term "biological control" was first used by [[Harry Scott Smith]] at the 1919 meeting of the Pacific Slope Branch of the American Association of Economic Entomologists, in [[Riverside, California]].<ref>{{cite web|url=http://biocontrol.ucr.edu/hoddle/harrysmithfund.html |title=Biological Control: Harry Smith Fund |access-date=2 March 2017 |url-status=live |archive-url=https://web.archive.org/web/20170421234114/http://biocontrol.ucr.edu/hoddle/harrysmithfund.html |archive-date=21 April 2017 }}</ref> It was brought into more widespread use by the entomologist Paul H. DeBach (1914–1993) who worked on citrus crop pests throughout his life.<ref>{{cite web|title=Inventory of the Paul H. DeBach Papers, 1921–1989 (bulk 1955–1980) |url=http://www.oac.cdlib.org/findaid/ark:/13030/kt2c60258h/ |publisher=Online Archive of California |access-date=7 April 2017 |url-status=live |archive-url=https://web.archive.org/web/20170408081537/http://www.oac.cdlib.org/findaid/ark%3A/13030/kt2c60258h/ |archive-date= 8 April 2017 }}</ref><ref>{{cite book |author=DeBach P., Hagen K. S. |date=1964 |title=Manipulation of entomophagous species |pages=429–458 |editor=P. DeBach |work=Biological control of insect pests and weeds |publisher=Reinhold}}</ref> However, the practice has previously been used for centuries. The first report of the use of an insect species to control an insect pest comes from "[[Nanfang Caomu Zhuang]]" (南方草木狀 ''Plants of the Southern Regions'') ({{circa|304 AD}}), attributed to [[Jin dynasty (265-420)|Western Jin dynasty]] botanist ''Ji Han'' (嵇含, 263–307), in which it is mentioned that "''[[Jiaozhi]] people sell ants and their nests attached to twigs looking like thin cotton envelopes, the reddish-yellow ant being larger than normal. Without such ants, southern citrus fruits will be severely insect-damaged''".<ref name="http-server.carleton.ca">{{cite journal |url=http://http-server.carleton.ca/~bgordon/Rice/papers/peng83.htm |title=Biological Control – One Of The Fine Traditions Of Ancient Chinese Agricultural Techniques |author=Peng, Shijiang |journal=Scientia Agricultura Sinica |date=1983 |volume=1 |pages=92–98 |url-status=dead |archive-url=https://web.archive.org/web/20161220073341/http://http-server.carleton.ca/~bgordon/Rice/papers/peng83.htm |archive-date=2016-12-20 }}</ref> The ants used are known as ''huang gan'' (''huang'' = yellow, ''gan'' = citrus) ants (''[[Oecophylla smaragdina]]''). The practice was later reported by Ling Biao Lu Yi (late [[Tang dynasty]] or Early [[Five Dynasties]]), in ''Ji Le Pian'' by ''Zhuang Jisu'' ([[Song dynasty|Southern Song dynasty]]), in the ''Book of Tree Planting'' by Yu Zhen Mu ([[Ming dynasty]]), in the book ''Guangdong Xing Yu'' (17th century), ''Lingnan'' by Wu Zhen Fang (Qing dynasty), in ''Nanyue Miscellanies'' by Li Diao Yuan, and others.<ref name="http-server.carleton.ca"/>

Biological control techniques as we know them today started to emerge in the 1870s. During this decade, in the US, the Missouri State Entomologist C. V. Riley and the Illinois State Entomologist W. LeBaron began within-state redistribution of parasitoids to control crop pests. The first international shipment of an insect as a biological control agent was made by Charles V. Riley in 1873, shipping to France the predatory mites ''Tyroglyphus phylloxera'' to help fight the grapevine phylloxera ([[Phylloxera|''Daktulosphaira vitifoliae'']]) that was destroying grapevines in France. The [[United States Department of Agriculture]] (USDA) initiated research in classical biological control following the establishment of the Division of Entomology in 1881, with C. V. Riley as Chief. The first importation of a parasitoidal wasp into the United States was that of the braconid ''[[Cotesia glomerata]]'' in 1883–1884, imported from Europe to control the invasive cabbage white butterfly, ''[[Pieris rapae]]''. In 1888–1889 the vedalia beetle, ''[[Novius cardinalis]]'', a lady beetle, was introduced from [[Australia]] to [[California]] to control the cottony cushion scale, ''[[Icerya purchasi]]''. This had become a major problem for the newly developed citrus industry in California, but by the end of 1889, the cottony cushion scale population had already declined. This great success led to further introductions of beneficial insects into the US.<ref name="Coulson J. R. 2000">Coulson, J. R.; Vail, P. V.; Dix M.E.; Nordlund, D.A.; Kauffman, W.C.; Eds. 2000. 110 years of biological control research and development in the United States Department of Agriculture: 1883–1993. U.S. Department of Agriculture, Agricultural Research Service. pages=3–11</ref><ref name=Berkeley>{{cite web |title=History and Development of Biological Control (notes) |access-date=10 April 2017 |publisher=University of California Berkeley |url=https://nature.berkeley.edu/biocon/BC%20Class%20Notes/6-11%20BC%20History.pdf |url-status=dead |archive-url=https://web.archive.org/web/20151124001647/http://nature.berkeley.edu/biocon/BC%20Class%20Notes/6-11%20BC%20History.pdf |archive-date=24 November 2015 }}</ref>

In 1905 the USDA initiated its first large-scale biological control program, sending entomologists to Europe and Japan to look for natural enemies of the spongy moth, ''[[Lymantria dispar dispar]]'', and the brown-tail moth, [[Brown-tail|''Euproctis chrysorrhoea'']], invasive pests of trees and shrubs. As a result, nine parasitoids (solitary wasps) of the spongy moth, seven of the brown-tail moth, and two predators of both moths became established in the US. Although the spongy moth was not fully controlled by these natural enemies, the frequency, duration, and severity of its outbreaks were reduced and the program was regarded as successful. This program also led to the development of many concepts, principles, and procedures for the implementation of biological control programs.<ref name="Coulson J. R. 2000"/><ref name=Berkeley/><ref>{{cite web|last1=Reardon |first1=Richard C. |title=Biological Control of The Gypsy Moth: An Overview |url=http://www.main.nc.us/SERAMBO/BControl/gypsy.html#conclu |website=Southern Appalachian Biological Control Initiative Workshop |access-date=10 April 2017 |url-status=live |archive-url=https://web.archive.org/web/20160905052259/http://www.main.nc.us/SERAMBO/BControl/gypsy.html |archive-date= 5 September 2016 }}</ref>

[[File:Larvaefeedingoncacti.jpg|thumb|upright|''[[Cactoblastis cactorum]]'' larvae feeding on ''[[Opuntia]]'' prickly pear cacti]]

[[Opuntia|Prickly pear cacti]] were introduced into [[Queensland]], Australia as ornamental plants, starting in 1788. They quickly spread to cover over 25&nbsp;million hectares of Australia by 1920, increasing by 1&nbsp;million hectares per year. Digging, burning, and crushing all proved ineffective. Two control agents were introduced to help control the spread of the plant, the cactus moth ''[[Cactoblastis cactorum]]'', and the scale insect ''[[Dactylopius]]''. Between 1926 and 1931, tens of millions of cactus moth eggs were distributed around Queensland with great success, and by 1932, most areas of prickly pear had been destroyed.<ref>{{cite web|url=https://www.daf.qld.gov.au/__data/assets/pdf_file/0014/55301/IPA-Prickly-Pear-Story-PP62.pdf |title=The Prickly Pear Story |publisher=Department of Agriculture and Fisheries, Queensland |access-date=7 June 2016 |url-status=live |archive-url=https://web.archive.org/web/20160610135855/https://www.daf.qld.gov.au/__data/assets/pdf_file/0014/55301/IPA-Prickly-Pear-Story-PP62.pdf |archive-date=10 June 2016 }}</ref>

The first reported case of a classical biological control attempt in [[Canada]] involves the parasitoidal wasp ''[[Trichogramma]] [[Trichogramma minutum|minutum]]''. Individuals were caught in [[New York State]] and released in [[Ontario]] gardens in 1882 by William Saunders, a trained chemist and first Director of the Dominion Experimental Farms, for controlling the invasive currantworm ''[[Nematus ribesii]]''. Between 1884 and 1908, the first Dominion Entomologist, James Fletcher, continued introductions of other parasitoids and pathogens for the control of pests in Canada.<ref>{{cite book |author=McLeod J. H., McGugan B. M., Coppel H. C. |date=1962 |title=A Review of the Biological Control Attempts Against Insects and Weeds in Canada. Technical Communication No. 2 |publisher=Commonwealth Agricultural Bureau |location=Reading, England}}</ref>

==Types of biological pest control==
There are three basic biological pest control strategies: importation (classical biological control), augmentation and conservation.<ref name=Cornell>{{Cite web|url=http://www.biocontrol.entomology.cornell.edu/what.html |publisher=Cornell University |title=What is Biological Control? |access-date=7 June 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160613054724/http://www.biocontrol.entomology.cornell.edu/what.html |archive-date=13 June 2016 }}</ref>

===Importation===

[[File:Vedalia Beetle (15959056801).jpg|thumb|left|''[[Rodolia cardinalis]]'', the vedalia beetle, was imported from Australia to California in the 19th century, successfully controlling [[cottony cushion scale]] on [[Orange (fruit)|orange]] trees.]]

Importation or classical biological control involves the introduction of a pest's natural enemies to a new locale where they do not occur naturally. Early instances were often unofficial and not based on research, and some introduced species became serious pests themselves.<ref name="Classical">{{cite web |title=Classical Biological Control: Importation of New Natural Enemies |url=http://www.entomology.wisc.edu/mbcn/fea103.html |publisher=University of Wisconsin |access-date=7 June 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160613023600/http://www.entomology.wisc.edu/mbcn/fea103.html |archive-date=13 June 2016 }}</ref>

To be most effective at controlling a pest, a biological control agent requires a colonizing ability which allows it to keep pace with changes to the habitat in space and time. Control is greatest if the agent has temporal persistence so that it can maintain its population even in the temporary absence of the target species, and if it is an opportunistic forager, enabling it to rapidly exploit a pest population.<ref name=follett>{{cite book |author1=Follett, P. A. |author2=Duan, J. J.  |date=2000 |title=Nontarget effects of biological control |publisher=Kluwer}}</ref>

One of the earliest successes was in controlling ''[[Icerya purchasi]]'' (cottony cushion scale) in Australia, using a predatory insect ''[[Rodolia cardinalis]]'' (the vedalia beetle). This success was repeated in California using the beetle and a parasitoidal fly, ''[[Cryptochaetum]] [[Cryptochaetum iceryae|iceryae]]''.<ref>{{cite web|title=How to Manage Pests. Cottony Cushion Scale |url=http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7410.html |publisher=University of California Integrated Pest Management |access-date=5 June 2016 |url-status=live |archive-url=https://web.archive.org/web/20160430061041/http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7410.html |archive-date=30 April 2016 }}</ref> Other successful cases include the control of ''[[Antonina graminis]]'' in Texas by ''[[Neodusmetia sangwani]]'' in the 1960s.<ref>{{Cite journal|doi=10.1146/annurev.en.26.010181.001241|title=Landmark Examples in Classical Biological Control|journal=Annual Review of Entomology|volume=26|pages=213–232|year=1981|last1=Caltagirone|first1=L. E.}}</ref>

Damage from ''[[Hypera postica]]'', the alfalfa weevil, a serious introduced pest of forage, was substantially reduced by the introduction of natural enemies. 20 years after their introduction the population of [[weevil]]s in the [[alfalfa]] area treated for alfalfa weevil in the [[Northeastern United States]] remained 75 percent down.<ref>{{cite web|title=How to Manage Pests. Alfalfa |url=http://www.ipm.ucdavis.edu/PMG/r1900211.html |publisher=University of California Integrated Pest Management |access-date=5 June 2016 |url-status=live |archive-url=https://web.archive.org/web/20160525013314/http://www.ipm.ucdavis.edu/PMG/r1900211.html |archive-date=25 May 2016 }}</ref>

[[Image:Alternanthera philoxeroides NRCS-1.jpg|thumb|The invasive species ''[[Alternanthera philoxeroides]]'' (alligator weed) was controlled in [[Florida]] (U.S.) by introducing [[Agasicles hygrophila|alligator weed flea beetle]].]]

[[Alligator weed]] was introduced to the United States from [[South America]]. It takes root in shallow water, interfering with [[navigation]], [[irrigation]], and [[flood control]]. The [[Agasicles hygrophila|alligator weed flea beetle]] and two other biological controls were released in [[Florida]], greatly reducing the amount of land covered by the plant.<ref>{{cite web|title=Indian River Lagoon Species Inventory: Alternanthera philoxeroides |url=http://www.sms.si.edu/irlspec/Alternanthera_philoxeroides.htm |publisher=Smithsonian Marine Station at Fort Pierce |access-date=9 April 2017 |date=1 December 2007 |url-status=live |archive-url=https://web.archive.org/web/20170328161203/http://www.sms.si.edu/irlspec/Alternanthera_philoxeroides.htm |archive-date=28 March 2017 }}</ref> Another aquatic weed, the giant salvinia (''[[Salvinia molesta]]'') is a serious pest, covering waterways, reducing water flow and harming native species. Control with the salvinia weevil (''[[Cyrtobagous salviniae]]'') and the salvinia stem-borer moth (''[[Samea multiplicalis]])'' is effective in warm climates,<ref>{{cite web|title=Salvinia (Salvinia molesta) |url=http://www.environment.gov.au/biodiversity/invasive/weeds/publications/guidelines/wons/pubs/s-molesta.pdf |publisher=CRC Weed Management |access-date=7 June 2016 |url-status=live |archive-url=https://web.archive.org/web/20150924073642/http://www.environment.gov.au/biodiversity/invasive/weeds/publications/guidelines/wons/pubs/s-molesta.pdf |archive-date=24 September 2015 }}</ref><ref>{{Cite web|url=https://www.invasive.org/proceedings/pdfs/6_543-549.pdf|title=A summary of research into biological control of salvinia in Australia}}</ref> and in Zimbabwe, a 99% control of the weed was obtained over a two-year period.<ref>{{cite journal |author1=Chikwenhere, Godfrey P. |author2=Keswani, C. L. |year=1997 |title=Economics of biological control of Kariba weed (''Salvinia molesta'' Mitchell) at Tengwe in north-western Zimbabwe: a case study |journal=International Journal of Pest Management |volume=43 |issue=2 |pages=109–112 |doi=10.1080/096708797228780 }}</ref>

Small, commercially-reared parasitoidal [[wasp]]s,<ref name=Cornell/> ''[[Trichogramma]] [[Trichogramma ostriniae|ostriniae]]'', provide limited and erratic control of the [[European corn borer]] (''Ostrinia nubilalis''), a serious pest. Careful formulations of the bacterium ''[[Bacillus thuringiensis]]'' are more effective. The O. nubilalis integrated control releasing  ''Tricogramma brassicae'' (egg parasitoid) and later ''Bacillus thuringiensis subs. kurstaki'' (larvicide effect) reduce pest damages more than insecticide treatments <ref>{{cite web|title=Featured Creatures. European corn borer |url=http://entnemdept.ufl.edu/creatures/field/e_corn_borer.htm |publisher=University of Florida IFAS |access-date=5 June 2016 |url-status=live |archive-url=https://web.archive.org/web/20160530041733/http://entnemdept.ufl.edu/creatures/field/e_corn_borer.htm |archive-date=30 May 2016 }}</ref>

The population of ''[[Levuana iridescens]]'', the Levuana moth, a serious coconut pest in [[Fiji]], was brought under control by a classical biological control program in the 1920s.<ref>{{cite journal |last1=Kuris |first1=Armand M. |title=Did biological control cause extinction of the coconut moth, Levuana iridescens, in Fiji? |journal=Biological Invasions|date=March 2003 |volume=5 |issue=1 |pages=133–141 |doi=10.1023/A:1024015327707|bibcode=2003BiInv...5..133K |s2cid=26094065 }}</ref>

===Augmentation===

[[File:Lady bugs are a beneficial insect commonly sold for biological control of aphids..jpg|thumb|''[[Hippodamia convergens]]'', the convergent lady beetle, is commonly sold for biological control of [[aphids]].]]

Augmentation involves the supplemental release of natural enemies that occur in a particular area, boosting the naturally occurring populations there. In inoculative release, small numbers of the control agents are released at intervals to allow them to reproduce, in the hope of setting up longer-term control and thus keeping the pest down to a low level, constituting prevention rather than cure. In inundative release, in contrast, large numbers are released in the hope of rapidly reducing a damaging pest population, correcting a problem that has already arisen. Augmentation can be effective, but is not guaranteed to work, and depends on the precise details of the interactions between each pest and control agent.<ref name="Augmentation">{{cite web |title=Augmentation: The Periodic Release of Natural Enemies |url=http://www.entomology.wisc.edu/mbcn/fea104.html |publisher=University of Wisconsin |access-date=7 June 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160317104655/http://www.entomology.wisc.edu/mbcn/fea104.html |archive-date=17 March 2016 }}</ref>

An example of inoculative release occurs in the horticultural production of several crops in [[greenhouse]]s. Periodic releases of the parasitoidal wasp, ''[[Encarsia formosa]]'', are used to control greenhouse [[whitefly]],<ref name=Hoddle1998/> while the predatory mite ''[[Phytoseiulus persimilis]]'' is used for control of the two-spotted spider mite.<ref>{{cite web |title=Biological control. Phytoseiulus persimilis (Acarina: Phytoseiidae) |url=http://www.biocontrol.entomology.cornell.edu/predators/Phytoseiulus.php |publisher=Cornell University |access-date=7 June 2016 |url-status=dead |archive-url=https://web.archive.org/web/20151115184109/http://www.biocontrol.entomology.cornell.edu/predators/Phytoseiulus.php |archive-date=15 November 2015 }}</ref>

The egg parasite ''[[Trichogramma]]'' is frequently released inundatively to control harmful moths. New way for inundative releases are now introduced i.e. use of drones. Egg parasitoids are able to find the eggs of the target host by means of several cues. Kairomones were found on moth scales. Similarly, ''Bacillus thuringiensis'' and other microbial insecticides are used in large enough quantities for a rapid effect.<ref name="Augmentation"/> Recommended release rates for ''Trichogramma'' in vegetable or field crops range from 5,000 to 200,000 per acre (1 to 50 per square metre) per week according to the level of pest infestation.<ref name="Peter2009">{{cite book|last=Peter |first=K. V. |title=Basics Of Horticulture |url=https://books.google.com/books?id=NWMa741kG_gC&pg=PA288 |year=2009 |publisher=New India Publishing |isbn=978-81-89422-55-4 |page=288 |url-status=live |archive-url=https://web.archive.org/web/20170407233649/https://books.google.com/books?id=NWMa741kG_gC&pg=PA288 |archive-date=2017-04-07 }}</ref> Similarly, [[nematodes]] that kill insects (that are entomopathogenic) are released at rates of millions and even billions per acre for control of certain soil-dwelling insect pests.<ref>{{cite web|title=Biological Control. Nematodes (Rhabditida: Steinernematidae & Heterorhabditidae) |url=http://www.biocontrol.entomology.cornell.edu/pathogens/nematodes.php |author1=Shapiro-Ilan, David I |author2=Gaugler, Randy |publisher=Cornell University |access-date=7 June 2016 |url-status=dead |archive-url=https://web.archive.org/web/20151215090802/http://www.biocontrol.entomology.cornell.edu/pathogens/nematodes.php |archive-date=15 December 2015 }}</ref>

===Conservation===

The conservation of existing natural enemies in an environment is the third method of biological pest control.<ref name="Conservation">{{cite web |title=Conservation of Natural Enemies: Keeping Your "Livestock" Happy and Productive |url=http://www.entomology.wisc.edu/mbcn/fea201.html |publisher=University of Wisconsin |access-date=7 June 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160318120526/http://www.entomology.wisc.edu/mbcn/fea201.html |archive-date=18 March 2016 }}</ref>
Natural enemies are already adapted to the [[habitat]] and to the target pest, and their conservation can be simple and cost-effective, as when nectar-producing crop plants are grown in the borders of rice fields. These provide nectar to support parasitoids and predators of planthopper pests and have been demonstrated to be so effective (reducing pest densities by 10- or even 100-fold) that farmers sprayed 70% less insecticides and enjoyed yields boosted by 5%.<ref>{{cite journal | last=Gurr | first=Geoff M. | title=Multi-country evidence that crop diversification promotes ecological intensification of agriculture | journal=Nature Plants | date=22 February 2016 | language=en | doi=10.1038/nplants.2016.14 | pmid=27249349 | volume=2 | issue=3 | page=16014| bibcode=2016NatPl...216014G | s2cid=205458366 }}</ref> Predators of aphids were similarly found to be present in tussock grasses by field boundary hedges in England, but they spread too slowly to reach the centers of fields. Control was improved by planting a meter-wide strip of tussock grasses in field centers, enabling aphid predators to overwinter there.<ref name="Conservation"/>

[[File:Dermaptera flowerpot.jpg|thumb|An inverted flowerpot filled with straw to attract [[Dermaptera|earwigs]]]]

Cropping systems can be modified to favor natural enemies, a practice sometimes referred to as habitat manipulation. Providing a suitable habitat, such as a [[Windbreak|shelterbelt]], [[hedgerow]], or [[beetle bank]] where beneficial insects such as parasitoidal wasps can live and reproduce, can help ensure the survival of populations of natural enemies. Things as simple as leaving a layer of fallen leaves or mulch in place provides a suitable food source for worms and provides a shelter for insects, in turn being a food source for such beneficial mammals as [[hedgehog]]s and [[shrew]]s. [[Compost pile]]s and stacks of wood can provide shelter for invertebrates and small mammals. Long grass and [[pond]]s support amphibians. Not removing dead annuals and non-hardy plants in the autumn allow insects to make use of their hollow stems during winter.<ref name="ReferenceA">{{cite book|author=Ruberson, John R. |title=Handbook of Pest Management |url=https://books.google.com/books?id=9b-9sIMbz38C&pg=PA428 |year=1999 |publisher=CRC Press |isbn=978-0-8247-9433-0 |pages=428–432 |url-status=live |archive-url=https://web.archive.org/web/20170410235857/https://books.google.com/books?id=9b-9sIMbz38C&pg=PA428 |archive-date=2017-04-10 }}</ref> In California, prune trees are sometimes planted in grape vineyards to provide an improved overwintering habitat or refuge for a key grape pest parasitoid.<ref>{{cite web |last1=Wilson |first1=L. Ted |last2=Pickett |first2=Charles H. |last3=Flaherty |first3=Donald L. |last4=Bates |first4=Teresa A. |title=French prune trees: refuge for grape leafhopper parasite |url=http://ucce.ucdavis.edu/files/repositoryfiles/ca4302p7-62179.pdf |publisher=University of California Davis |access-date=7 June 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160923154830/http://ucce.ucdavis.edu/files/repositoryfiles/ca4302p7-62179.pdf |archive-date=23 September 2016 }}</ref> The providing of artificial shelters in the form of wooden caskets, [[box]]es or [[flowerpot]]s is also sometimes undertaken, particularly in gardens, to make a cropped area more attractive to natural enemies. For example, [[Dermaptera|earwigs]] are natural predators that can be encouraged in gardens by hanging upside-down flowerpots filled with [[straw]] or [[wood wool]]. Green [[lacewings]] can be encouraged by using plastic bottles with an open bottom and a roll of cardboard inside. Birdhouses enable insectivorous birds to nest; the most useful birds can be attracted by choosing an opening just large enough for the desired species.<ref name="ReferenceA"/>

In cotton production, the replacement of broad-spectrum insecticides with selective control measures such as [[Bt cotton]] can create a more favorable environment for natural enemies of cotton pests due to reduced insecticide exposure risk. Such predators or [[parasitoids]] can control pests not affected by the [[Bacillus thuringiensis|Bt protein]]. Reduced prey quality and abundance associated with increased control from Bt cotton can also indirectly decrease natural enemy populations in some cases, but the percentage of pests eaten or parasitized in Bt and non-Bt cotton are often similar.<ref>{{cite journal|last1=Naranjo|first1=Steven E.|title=Impacts of Transgenic Cotton on Integrated Pest Management|journal=Journal of Agricultural and Food Chemistry|date=8 June 2011|volume=59|issue=11|pages=5842–5851|doi=10.1021/jf102939c|pmid=20942488|doi-access=free|bibcode=2011JAFC...59.5842N }}</ref>

==Biological control agents==

===Predators===
[[File:Chrysopidae 3035.jpg|thumb|left|[[Predator]]y [[Chrysopidae|lacewings]] are available from biocontrol dealers.]]

Predators are mainly free-living species that directly consume a large number of [[prey]] during their whole lifetime. Given that many major crop pests are insects, many of the predators used in biological control are insectivorous species. [[Ladybugs|Lady beetles]], and in particular their larvae which are active between May and July in the northern hemisphere, are voracious predators of [[aphid]]s, and also consume [[mites]], [[scale insect]]s and small [[caterpillar]]s. The spotted lady beetle (''[[Coleomegilla maculata]]'') is also able to feed on the eggs and larvae of the [[Colorado potato beetle]] (''Leptinotarsa decemlineata'').<ref>{{cite book |author=Acorn, John |title=Ladybugs of Alberta: Finding the Spots and Connecting the Dots |url=https://archive.org/details/ladybugsofalbert00acor |url-access=registration |year=2007 |publisher=University of Alberta |isbn=978-0-88864-381-0 |page=[https://archive.org/details/ladybugsofalbert00acor/page/15 15]}}</ref>

The larvae of many [[hoverfly]] species principally feed upon [[aphid]]s, one larva devouring up to 400 in its lifetime. Their effectiveness in commercial crops has not been studied.<ref>{{cite web |title=Know Your Friends. Hover Flies |url=http://www.entomology.wisc.edu/mbcn/kyf211.html |publisher=University of Wisconsin |access-date=7 June 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160604163106/http://www.entomology.wisc.edu/mbcn/kyf211.html |archive-date=4 June 2016 }}</ref>

The running crab spider ''[[Philodromus cespitum]]'' also prey heavily on aphids, and act as a biological control agent in European fruit orchards.<ref>Michalko, Radek; Dvoryankina, Viktoriya (1 June 2019). "Intraspecific phenotypic variation in functional traits of a generalist predator in an agricultural landscape". ''Agriculture, Ecosystems & Environment''. '''278''': 35–42. [[Doi (identifier)|doi]]:10.1016/j.agee.2019.03.018.</ref>

[[File:Organic-agriculture biocontrol-cotton polistes-wasp3.png|thumb|[[Predator]]y ''[[Paper wasp|Polistes]]'' [[Vespid|wasp]] searching for bollworms or other [[caterpillar]]s on a cotton plant]]

Several species of [[entomopathogenic nematode]] are important predators of insect and other invertebrate pests.<ref>{{cite book |author=Kaya, Harry K. |chapter=An Overview of Insect-Parasitic and Entomopathogenic Nematodes |editor=Bedding, R.A. |title=Nematodes and the Biological Control of Insect Pests |publisher=CSIRO Publishing |year=1993 |isbn=978-0-643-10591-1 |chapter-url=https://books.google.com/books?id=drhdg7UmNnAC&pg=PT8 |pages=8–12 |display-authors=etal |url-status=live |archive-url=https://web.archive.org/web/20160512141401/https://books.google.com/books?id=drhdg7UmNnAC&pg=PT8 |archive-date=12 May 2016}}</ref><ref name=Capinera1992>{{Cite journal |last1=Capinera |first1=John L. |last2=Epsky |first2=Nancy D. |date=1992-01-01 |title=Potential for Biological Control of Soil Insects in the Caribbean Basin Using Entomopathogenic Nematodes |journal=The Florida Entomologist |volume=75 |issue=4 |pages=525–532 |jstor=3496134 |doi=10.2307/3496134}}</ref> Entomopathogenic nematodes form a stress–resistant stage known as the infective juvenile. These spread in the soil and infect suitable insect hosts. Upon entering the insect they move to the [[hemolymph]] where they recover from their stagnated state of development and release their [[Photorhabdus|bacterial]] [[Symbiosis|symbionts]]. The bacterial symbionts reproduce and release toxins, which then kill the host insect.<ref name=Capinera1992/><ref name=Campos2015>{{cite book |title=Nematode Pathogenesis of insects and other pests |date=2015 |publisher=Springer |isbn=978-3-319-18266-7 |edition=1 |pages=4–6, 31–32 |last=Campos |first=Herrera R. |editor1-first=Raquel |editor1-last=Campos-Herrera |doi=10.1007/978-3-319-18266-7|hdl=11586/145351 |s2cid=27605492 }}</ref> ''[[Phasmarhabditis hermaphrodita]]'' is a microscopic [[nematode]] that kills slugs. Its complex life cycle includes a free-living, infective stage in the soil where it becomes associated with a pathogenic bacteria such as ''[[Moraxella osloensis]]''. The nematode enters the slug through the posterior mantle region, thereafter feeding and reproducing inside, but it is the bacteria that kill the slug. The nematode is available commercially in Europe and is applied by watering onto moist soil.<ref>{{cite web |url=http://www.biocontrol.entomology.cornell.edu/pathogens/phasmarhabditis.php |title=Biological control: ''Phasmarhabditis hermaphrodita'' |publisher=Cornell University |access-date=15 June 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160618025012/http://www.biocontrol.entomology.cornell.edu/pathogens/phasmarhabditis.php |archive-date=18 June 2016 }}</ref> Entomopathogenic nematodes have a limited [[shelf life]] because of their limited resistance to high temperature and dry conditions.<ref name=Campos2015/> The type of soil they are applied to may also limit their effectiveness.<ref name=Capinera1992/>

Species used to control spider mites include the predatory mites ''[[Phytoseiulus persimilis]]'',<ref>{{cite web |title=Glasshouse red spider mite |url=https://www.rhs.org.uk/advice/profile?PID=190 |publisher=[[Royal Horticultural Society]] |access-date=7 June 2016 |url-status=live |archive-url=https://web.archive.org/web/20160614161933/https://www.rhs.org.uk/advice/profile?PID=190 |archive-date=14 June 2016 }}</ref> ''[[Neoseilus]] [[Neoseilus californicus|californicus]],''<!--aka Amblyseius--><ref name=UConnMites/> and ''[[Amblyseius]] [[Amblyseius cucumeris|cucumeris]]'', the predatory midge ''[[Feltiella acarisuga]]'',<ref name=UConnMites>{{cite web |title=Biological Control of Two- Spotted Spider Mites |url=http://ipm.uconn.edu/documents/raw2/html/664.php?aid=664 |publisher=University of Connecticut |access-date=7 June 2016 |url-status=live |archive-url=https://web.archive.org/web/20160807023211/http://ipm.uconn.edu/documents/raw2/html/664.php?aid=664 |archive-date= 7 August 2016 }}</ref> and a ladybird ''[[Stethorus punctillum]]''.<ref name=UConnMites/> The bug ''[[Orius insidiosus]]'' has been successfully used against the [[Tetranychus urticae|two-spotted spider mite]] and the [[western flower thrips]] (''Frankliniella occidentalis'').<ref>{{cite book |author=Xuenong Xu |title=Combined Releases of Predators for Biological Control of Spider Mites ''Tetranychus urticae'' Koch and Western Flower Thrips ''Frankliniella occidentalis'' (Pergande) |url=https://books.google.com/books?id=y6DGyV7HmqAC&pg=PA37 |year=2004 |publisher=Cuvillier Verlag |isbn=978-3-86537-197-3 |page=37}}</ref>

Predators including ''Cactoblastis cactorum'' (mentioned above) can also be used to destroy invasive plant species. As another example, the [[Agonopterix alstroemeriana|poison hemlock moth]] (''Agonopterix alstroemeriana)'' can be used to control [[Conium maculatum|poison hemlock]] (''Conium maculatum''). During its larval stage, the moth strictly consumes its host plant, poison hemlock, and can exist at hundreds of larvae per individual host plant, destroying large swathes of the hemlock.<ref>{{Cite journal |last1=Castells |first1=Eva |last2=Berenbaum |first2=May R. |date=June 2006 |title=Laboratory Rearing of Agonopterix alstroemeriana, the Defoliating Poison Hemlock (Conium maculatum L.) Moth, and Effects of Piperidine Alkaloids on Preference and Performance |journal=Environmental Entomology |volume=35 |issue=3 |pages=607–615 |doi=10.1603/0046-225x-35.3.607|s2cid=45478867 |url=https://ddd.uab.cat/pub/artpub/2006/125702/2006_alstroemeriana_rearing.pdf }}</ref>

[[File:Aleiodes indiscretus wasp parasitizing gypsy moth caterpillar.jpg|thumb|The [[parasitoid wasp]] ''[[Aleiodes|Aleiodes indiscretus]]'' parasitizing a [[spongy moth]] caterpillar, a serious pest of forestry<ref>{{cite web | url=http://sfec.cfans.umn.edu/prod/groups/cfans/@pub/@cfans/@sfec/documents/article/cfans_article_380545.pdf | title=European Gypsy Moth (Lymantria dispar) | access-date=3 December 2017 | url-status=dead | archive-url=https://web.archive.org/web/20130517073305/http://sfec.cfans.umn.edu/prod/groups/cfans/@pub/@cfans/@sfec/documents/article/cfans_article_380545.pdf | archive-date=17 May 2013}}</ref>]]

For [[Rodent#As pests and disease vectors|rodent pests]], [[Farm cat|cat]]s are effective biological control when used in conjunction with reduction of [[Refuge (ecology)|"harborage"/hiding]] locations.<ref>{{cite journal |title=The Use of Food as a Buffer in a Predator-Prey System |first=David E. |last=Davis |date=20 November 1957 |journal=Journal of Mammalogy |volume=38 |issue=4 |pages=466–472 |doi=10.2307/1376399 |jstor=1376399 }}</ref><ref name="Lambert">{{cite thesis |type=PhD |last1=Lambert |first1=Mark |title=Control Of Norway Rats In The Agricultural Environment: Alternatives To Rodenticide Use |url=https://lra.le.ac.uk/bitstream/2381/27745/1/2003LambertMSPhD.pdf |publisher=University of Leicester |pages=85–103 |format=Thesis |date=September 2003 |access-date=2017-11-11 |archive-date=2017-11-11 |archive-url=https://web.archive.org/web/20171111151737/https://lra.le.ac.uk/bitstream/2381/27745/1/2003LambertMSPhD.pdf |url-status=dead }}</ref><ref name="Wodzicki">{{cite journal |title=Prospects for biological control of rodent populations |first=Kazimierz |last=Wodzicki |date=11 November 1973 |journal=Bulletin of the World Health Organization |volume=48 |issue=4 |pages=461–467 |pmid=4587482 |pmc=2481104}}</ref> While cats are effective at preventing rodent [[Irruptive growth|"population explosions"]], they are not effective for eliminating pre-existing severe infestations.<ref name="Wodzicki"/> [[Western barn owl|Barn owls]] are also sometimes used as biological rodent control.<ref name=Charter>{{cite web |url=http://www.owls.org/conservation/ewExternalFiles/barn_owls_in_israel.pdf |title=Using barn owls (''Tyto alba erlangeri'') for biological pest control in Israel |author=Charter, Motti |publisher=World Owl Trust |access-date=11 November 2017 |archive-url=https://web.archive.org/web/20171111095113/http://www.owls.org/conservation/ewExternalFiles/barn_owls_in_israel.pdf |archive-date=2017-11-11 |url-status=dead }}</ref> Although there are no quantitative studies of the effectiveness of barn owls for this purpose,<ref>{{cite journal |title=Are avian predators effective biological control agents for rodent pest management in agricultural systems? |first1=Lushka |last1=Labuschagne |first2=Lourens H. |last2=Swanepoel |first3=Peter J |last3=Taylor |first4=Steven R. |last4=Belmain |first5=Mark |last5=Keith |date=1 October 2016 |journal=Biological Control |volume=101 |issue=Supplement C |pages=94–102 |doi=10.1016/j.biocontrol.2016.07.003|bibcode=2016BiolC.101...94L |url=http://gala.gre.ac.uk/15648/23/15648%20BELMAIN_Avian_Predators_13-06-2016.pdf |hdl=10019.1/111721 |hdl-access=free }}</ref> they are known rodent predators that can be used in addition to or instead of cats;<ref>{{Cite book|url=https://books.google.com/books?id=4ddfAQAAQBAJ&pg=PA141 |title=Crop Protection in Medieval Agriculture: Studies in pre-modern organic agriculture |first=Jan C. |last=Zadoks | author-link=Jan Zadoks|date=16 October 2013 |publisher=Sidestone Press |access-date=11 November 2017 |via=Google Books|isbn=9789088901874 }}</ref><ref>{{cite web |url=https://attra.ncat.org/how_can_i_control_rodents_organically/ |title=How can I control rodents organically? |publisher=ATTRA - National Sustainable Agriculture Information Service |access-date=11 November 2017 |archive-date=17 October 2021 |archive-url=https://web.archive.org/web/20211017132940/https://attra.ncat.org/how_can_i_control_rodents_organically/ |url-status=dead }}</ref> they can be encouraged into an area with nest boxes.<ref>{{cite journal |title=Agricultural land use, barn owl diet, and vertebrate pest control implications |first1=Sara M. |last1=Kross |first2=Ryan P. |last2=Bourbour |first3=Breanna L. |last3=Martinico |date=1 May 2016 |journal=Agriculture, Ecosystems & Environment |volume=223 |issue=Supplement C |pages=167–174 |doi=10.1016/j.agee.2016.03.002|bibcode=2016AgEE..223..167K }}</ref><ref>{{cite web |url=https://www.barnowltrust.org.uk/barn-owl-facts/barn-owl-home-range/ |title=Barn Owl home range |publisher=The Barn Owl Trust |access-date=11 November 2017}}</ref>

In Honduras, where the mosquito ''[[Aedes aegypti]]'' was transmitting [[dengue fever]] and other infectious diseases, biological control was attempted by a community action plan; [[copepod]]s, baby [[turtle]]s, and juvenile [[tilapia]] were added to the wells and tanks where the mosquito breeds and the mosquito larvae were eliminated.<ref>{{cite web |url=http://ecotippingpoints.org/our-stories/indepth/honduras-community-eradication-aedes-aegypti-dengue-zika.html |title=The Monte Verde Story (Honduras): Community Eradication of Aedes aegypti (the mosquito responsible for Zika, dengue fever, and chikungunya) |author= Marten, Gerry; Caballero, Xenia; Romero, Hilda; Larios, Arnulfo |date=1 January 2019 |publisher=The EcoTipping Point Project  |access-date=30 January 2020}}</ref>

Even amongst arthropods usually thought of as obligate [[predator]]s of animals (especially other arthropods), [[flower|floral]] food sources ([[nectar]] and to a lesser degree [[pollen]]) are often useful adjunct sources.<ref name="He-et-al-2021" /> It had been noticed in one study<ref name="He-Sigsgaard-2019" /> that adult ''[[Adalia bipunctata]]'' (predator and common biocontrol of ''[[Mediterranean flour moth|Ephestia kuehniella]]'') could survive on flowers but never completed its [[biological life cycle|life cycle]], so a meta-analysis<ref name="He-et-al-2021" /> was done to find such an overall trend in previously published data, if it existed. In some cases floral resources are outright necessary.<ref name="He-et-al-2021" /> Overall, floral resources (and an imitation, i.e. sugar water) increase [[longevity]] and [[fecundity]], meaning even predatory population numbers can depend on non-prey food abundance.<ref name="He-et-al-2021" /> Thus biocontrol population maintenance – and success – may depend on nearby flowers.<ref name="He-et-al-2021" />

===Parasitoids===
{{main|Parasitoid}}

Parasitoids lay their eggs on or in the body of an insect host, which is then used as a food for developing larvae. The host is ultimately killed. Most insect [[parasitoid]]s are [[Parasitoid wasp|wasps]] or [[Fly|flies]], and many have a very narrow host range. The most important groups are the [[Ichneumonidae|ichneumonid wasps]], which mainly use [[caterpillar]]s as hosts; [[Braconidae|braconid wasps]], which attack caterpillars and a wide range of other insects including aphids; [[chalcid wasp|chalcidoid wasps]], which parasitize eggs and larvae of many insect species; and [[Tachinidae|tachinid flies]], which parasitize a wide range of insects including caterpillars, [[beetle]] adults and larvae, and [[Hemiptera|true bugs]].<ref>{{cite web|title=Parasitoid Wasps (Hymenoptera) |url=https://extension.umd.edu/hgic/insects/parasitoid-wasps-hymenoptera |publisher=University of Maryland |access-date=6 June 2016 |url-status=live |archive-url=https://web.archive.org/web/20160827072031/https://extension.umd.edu/hgic/insects/parasitoid-wasps-hymenoptera |archive-date=27 August 2016}}</ref> Parasitoids are most effective at reducing pest populations when their host organisms have limited [[refuge (ecology)|refuges]] to hide from them.<ref name="HawkinsThomas1993">{{cite journal |last1=Hawkins |first1=B. A. |last2=Thomas |first2=M. B. |last3=Hochberg |first3=M. E. |title=Refuge Theory and Biological Control |journal=Science |volume=262 |issue=5138 |year=1993 |pages=1429–1432 |doi=10.1126/science.262.5138.1429 |pmid=17736826|bibcode=1993Sci...262.1429H |s2cid=45268030 }}</ref>

[[File:Encarsia formosa, an endoparasitic wasp, is used for whitefly control.jpg|thumb|''[[Encarsia formosa]]'', widely used in [[greenhouse]] horticulture, was one of the first biological control agents developed.]]
[[File:Waspcycle.png|thumb|right|450px|Life cycles of greenhouse whitefly and its parasitoid wasp ''[[Encarsia formosa]]'']]

Parasitoids are among the most widely used biological control agents. Commercially, there are two types of rearing systems: short-term daily output with high production of parasitoids per day, and long-term, low daily output systems.<ref name=smith>{{cite journal |author=Smith, S.M. |date=1996 |title=Biological control with Trichogramma: advances, successes, and potential of their use |journal=Annual Review of Entomology |volume=41 |pages=375–406 |pmid=15012334 |doi=10.1146/annurev.en.41.010196.002111}}</ref> In most instances, production will need to be matched with the appropriate release dates when susceptible host species at a suitable phase of development will be available.<ref>{{cite journal |author1= Knoll, Valery |author2=Ellenbroek, Thomas |author3=Romeis, Jörg |author4=Collatz, Jana  |year=2017 |title=Seasonal and regional presence of hymenopteran parasitoids of ''Drosophila'' in Switzerland and their ability to parasitize the invasive ''Drosophila suzukii'' |journal=Scientific Reports |volume=7 |issue=40697 |pages=40697 |doi=10.1038/srep40697 |pmid=28098183 |pmc=5241644 |bibcode=2017NatSR...740697K }}</ref> Larger production facilities produce on a yearlong basis, whereas some facilities produce only seasonally. Rearing facilities are usually a significant distance from where the agents are to be used in the field, and transporting the parasitoids from the point of production to the point of use can pose problems.<ref>{{cite book|author1=Sithanantham, S. |author2=Ballal, Chandish R. |author3=Jalali, S.K. |author4=Bakthavatsalam, N. |title=Biological Control of Insect Pests Using Egg Parasitoids |url=https://books.google.com/books?id=cCO4BAAAQBAJ&pg=PA246 |year=2013 |publisher=Springer |isbn=978-81-322-1181-5 |page=246 |url-status=live |archive-url=https://web.archive.org/web/20170410133425/https://books.google.com/books?id=cCO4BAAAQBAJ&pg=PA246 |archive-date=10 April 2017}}</ref> Shipping conditions can be too hot, and even vibrations from planes or trucks can adversely affect parasitoids.<ref name=smith/>

''[[Encarsia formosa]]'' is a small parasitoid wasp attacking [[whitefly|whiteflies]], sap-feeding insects which can cause wilting and [[Sooty mold|black sooty moulds]] in glasshouse vegetable and ornamental crops. It is most effective when dealing with low level infestations, giving protection over a long period of time. The wasp lays its eggs in young whitefly 'scales', turning them black as the parasite larvae pupate.<ref name=Hoddle1998>{{cite journal |title=Biology and Use of the Whitefly Parasitoid Encarsia Formosa |author1=Hoddle, M. S. |author2=Van Driesche, R. G. |author3=Sanderson, J. P. |date=1998 |journal=Annual Review of Entomology |volume=43 |pages=645–669 |doi=10.1146/annurev.ento.43.1.645 |pmid=15012401 }}</ref> ''[[Gonatocerus ashmeadi]]'' ([[Hymenoptera]]: [[Mymaridae]]) has been introduced to control the [[glassy-winged sharpshooter]] ''Homalodisca vitripennis'' (Hemiptera: [[Cicadellidae]]) in [[French Polynesia]] and has successfully controlled ~95% of the pest density.<ref name=Hoddle2006>{{cite journal |author1=Hoddle M. S. |author2=Grandgirard J. |author3=Petit J. |author4=Roderick G. K. |author5=Davies N. | year=2006 | title=Glassy-winged sharpshooter Ko'ed – First round – in French Polynesia | journal=Biocontrol News and Information | volume=27 | issue=3 | pages=47N–62N}}</ref>

The [[Choristoneura fumiferana|eastern spruce budworm]] is an example of a destructive insect in [[fir]] and [[spruce]] forests. Birds are a natural form of biological control, but the ''Trichogramma minutum'', a species of parasitic wasp, has been investigated as an alternative to more controversial chemical controls.<ref name="smith2">{{Cite journal | doi=10.1111/j.1439-0418.1986.tb00830.x|title = Factors affecting inundative releases of ''Trichogramma'' minutum ''Ril''. Against the Spruce Budworm| journal=Journal of Applied Entomology| volume=101| issue=1–5| pages=29–39|year = 1986|last1 = Smith|first1 = S. M.| last2=Hubbes| first2=M.| last3=Carrow| first3=J. R.|s2cid = 84398725}}</ref>

There are a number of recent studies pursuing sustainable methods for controlling urban cockroaches using parasitic wasps.<ref>{{cite journal |last1=Bressan-Nascimento |first1=S. |last2=Oliveira |first2=D.M.P. |last3=Fox |first3=E.G.P. |title=Thermal requirements for the embryonic development of Periplaneta americana (L.) (Dictyoptera: Blattidae) with potential application in mass-rearing of egg parasitoids |journal=Biological Control |date=December 2008 |volume=47 |issue=3 |pages=268–272 |doi=10.1016/j.biocontrol.2008.09.001|bibcode=2008BiolC..47..268B }}</ref><ref>{{cite journal |last1=Paterson Fox |first1=Eduardo Gonçalves |last2=Bressan-Nascimento |first2=Suzete |last3=Eizemberg |first3=Roberto |title=Notes on the Biology and Behaviour of the Jewel Wasp, Ampulex compressa (Fabricius, 1781) (Hymenoptera; Ampulicidae), in the Laboratory, Including First Record of Gregarious Reproduction |journal=Entomological News |date=September 2009 |volume=120 |issue=4 |pages=430–437 |doi=10.3157/021.120.0412|s2cid=83564852 }}</ref> Since most cockroaches remain in the sewer system and sheltered areas which are inaccessible to insecticides, employing active-hunter wasps is a strategy to try and reduce their populations.

===Pathogens===
{{Further|Biopesticide}}

Pathogenic micro-organisms include [[bacteria]], [[fungi]], and [[viruses]]. They kill or debilitate their host and are relatively host-specific. Various [[microbial]] insect diseases occur naturally, but may also be used as [[biological pesticide]]s.<ref>[http://ec.europa.eu/environment/integration/research/newsalert/pdf/134na5.pdf Encouraging innovation in biopesticide development.] {{webarchive |url=https://web.archive.org/web/20120515143828/http://ec.europa.eu/environment/integration/research/newsalert/pdf/134na5.pdf |date=15 May 2012}} European Commission (2008). Accessed on 9 January 2017</ref> When naturally occurring, these outbreaks are density-dependent in that they generally only occur as insect populations become denser.<ref>{{cite book |author1=Huffaker, C. B. |author2=Berryman, A. A. |author3=Laing, J. E. |date=1984 |chapter=Natural control of insect populations |pages=[https://archive.org/details/ecologicalentomo0000unse/page/359 359–398] |editor=C. B. Huffaker and R. L. Rabb |title=Ecological Entomology |publisher=Wiley Interscience |isbn=978-0-471-06493-0 |chapter-url=https://archive.org/details/ecologicalentomo0000unse |url=https://archive.org/details/ecologicalentomo0000unse/page/359 }}</ref>

The use of pathogens against [[aquatic weed]]s was unknown until a groundbreaking 1972 proposal by Zettler and Freeman. Up to that point biocontrol of any kind had not been used against any water weeds. In their review of the possibilities, they noted the lack of interest and information thus far, and listed what was known of pests-of-pests – whether pathogens or not. They proposed that this should be relatively straightforward to apply in the same way as other biocontrols.<ref name="Zettler-Freeman-1972">{{cite journal | last1=Zettler | first1=F W | last2=Freeman | first2=T E | title=Plant Pathogens as Biocontrols of Aquatic Weeds | journal=[[Annual Review of Phytopathology]] | publisher=[[Annual Reviews (publisher)|Annual Reviews]] | volume=10 | issue=1 | year=1972 | issn=0066-4286 | doi=10.1146/annurev.py.10.090172.002323 | pages=455–470| bibcode=1972AnRvP..10..455Z }}</ref> And indeed in the decades since, the same biocontrol methods that are routine on land have become common in the water.

====Bacteria====

Bacteria used for biological control infect insects via their digestive tracts, so they offer only limited options for controlling insects with sucking mouth parts such as aphids and scale insects.<ref>{{cite book |author=Swan, L.A. |date=1964 |title=Beneficial Insects |url=https://archive.org/details/beneficialinsect0000swan |url-access=registration |page= [https://archive.org/details/beneficialinsect0000swan/page/249 249]|publisher=New York, Harper & Row }}</ref> ''[[Bacillus thuringiensis]]'', a soil-dwelling bacterium, is the most widely applied species of bacteria used for biological control, with at least four sub-species used against [[Lepidoptera]]n ([[moth]], [[butterfly]]), [[Coleoptera]]n (beetle) and [[Diptera]]n (true fly) insect pests. The bacterium is available to organic farmers in sachets of dried spores which are mixed with water and sprayed onto vulnerable plants such as [[brassica]]s and [[fruit tree]]s.<ref name=Lemaux>{{cite journal |doi=10.1146/annurev.arplant.58.032806.103840 |title=Genetically Engineered Plants and Foods: A Scientist's Analysis of the Issues (Part I) |year=2008 |last1=Lemaux |first1=Peggy G. |journal=Annual Review of Plant Biology |volume=59 |issue=1 |pages=771–812 |pmid=18284373|bibcode=2008AnRPB..59..771L }}</ref><ref name=McGaughey>{{cite journal | last1 = McGaughey | first1 = W. H. | last2 = Gould | first2 = F. | last3 = Gelernter | first3 = W. | year = 1998 | title = Bt resistance management | journal = Nat. Biotechnol. | volume = 16 | issue = 2| pages = 144–6 | doi = 10.1038/nbt0298-144 | pmid = 9487517 | s2cid = 37947689 }}</ref> [[Gene]]s from ''B. thuringiensis'' have also been incorporated into [[Genetically modified crops|transgenic crops]], making the plants express some of the bacterium's toxins, which are [[protein]]s. These confer resistance to insect pests and thus reduce the necessity for pesticide use.<ref name=Kumar>{{Cite book| last1=Kumar | first1=PA | last2=Malik | first2=VS | last3=Sharma | first3=RP | year=1996 | title=Insecticidal proteins of Bacillus thuringiensis | journal=Advances in Applied Microbiology | volume=42 | pages=1–43 | doi=10.1016/S0065-2164(08)70371-X | pmid=8865583 | isbn=9780120026425  | url=https://zenodo.org/record/1259743 }}</ref> If pests develop resistance to the toxins in these crops, ''B. thuringiensis'' will become useless in organic farming also.<ref>{{cite web|last1=Neppl |first1=Camilla |title=Management of Resistance to Bacillus thuringiensis Toxins |url=http://camillapede.tripod.com/bapaper.html |date=26 May 2000 |url-status=live |archive-url=https://web.archive.org/web/20170421000124/http://camillapede.tripod.com/bapaper.html |archive-date=21 April 2017 }}</ref><ref name=McGaughey/>
The bacterium ''[[Paenibacillus popilliae]]'' which causes [[Milky spore|milky spore disease]] has been found useful in the control of [[Japanese beetle]], killing the larvae. It is very specific to its host species and is harmless to vertebrates and other invertebrates.<ref>{{cite web|url=http://www.biocontrol.entomology.cornell.edu/pathogens/paenibacillus.php |title=Biological control: ''Paenibacillus popilliae'' |publisher=Cornell University |access-date=15 June 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160621024151/http://www.biocontrol.entomology.cornell.edu/pathogens/paenibacillus.php |archive-date=21 June 2016 }}</ref>

''[[Bacillus]]'' spp.,<ref group="M" name="biocontrol-MoAs">p.{{nbs}}94-5, II. Biocontrol Modes of Action</ref> [[fluorescent Pseudomonad]]s,<ref group="M" name="biocontrol-MoAs" /> and [[Streptomycete]]s are controls of various fungal pathogens.<ref group="M" name="intro-examples-agents">p.{{nbs}}94</ref>

==== Colombia mosquito control ====
The largest-ever deployment of ''[[Wolbachia]]''-infected ''A. aegypti'' mosquitoes reduced dengue incidence by 94–97% in the Colombian cities of [[Bello, Antioquia|Bello]], [[Medellín]], and [[Itagüí]]. The project was executed by non-profit World Mosquito Program (WMP). Wolbachia prevents mosquitos from transmitting viruses such as dengue and [[zika]]. The insects pass the bacteria on to their offspring. The project covered a combined area of {{Convert|135|km2}}, home to 3.3 million people. Most of the project area reached the target of infecting 60% of local mosquitoes. The technique is not endorsed by WHO.<ref>{{Cite journal |last=Lenharo |first=Mariana |date=2023-10-27 |title=Dengue rates drop after release of modified mosquitoes in Colombia |url=https://www.nature.com/articles/d41586-023-03346-2 |journal=Nature |volume=623 |issue=7986 |pages=235–236 |language=en |doi=10.1038/d41586-023-03346-2|pmid=37891252 |bibcode=2023Natur.623..235L |s2cid=264543032 }}</ref>

=== Fungi ===
[[File:Pandora neoaphidis.jpg|thumb|right|[[Green peach aphid]], a pest in its own right and a vector of plant viruses, killed by the fungus ''[[Pandora neoaphidis]]'' ([[Zygomycota]]: [[Entomophthorales]]) Scale bar = 0.3 mm.]]

[[Entomopathogenic fungi]], which cause disease in insects, include at least 14 species that attack [[aphid]]s.<ref>{{cite journal |author1=Hall, I.M. |author2=Dunn, P.H.  |title=Entomophthorous Fungi Parasitic on the Spotted Alfalfa Aphid |journal=Hilgardia |date=1957 |volume=27 |issue=4 |pages=159–181 |doi=10.3733/hilg.v27n04p159|doi-access=free }}</ref> ''[[Beauveria bassiana]]'' is mass-produced and used to manage a wide variety of insect pests including [[whiteflies]], [[thrips]], aphids and [[weevils]].<ref name=McNeil>{{cite web|last1=McNeil |first1=Jim |title=Fungi for the biological control of insect pests |url=http://articles.extension.org/pages/18928/fungi-for-the-biological-control-of-insect-pests |publisher=eXtension.org |access-date=6 June 2016 |date=2016 |url-status=live |archive-url=https://web.archive.org/web/20160526163616/http://articles.extension.org/pages/18928/fungi-for-the-biological-control-of-insect-pests |archive-date=26 May 2016 }}</ref> ''[[Lecanicillium]]'' spp. are deployed against white flies, thrips and aphids. ''[[Metarhizium]]'' spp. are used against pests including beetles, [[locusts]] and other grasshoppers, [[Hemiptera]], and [[spider mite]]s. ''[[Paecilomyces fumosoroseus]]'' is effective against white flies, thrips and aphids; ''[[Purpureocillium]] lilacinus'' is used against [[root-knot nematodes]], and 89 ''[[Trichoderma]]'' [[List of Trichoderma species|species]] against certain plant pathogens.<ref group="M" name="Trichoderma">p.{{nbs}}93</ref> ''[[Trichoderma viride]]'' has been used against [[Dutch elm disease]], and has shown some effect in suppressing [[Chondrostereum purpureum|silver leaf]], a disease of stone fruits caused by the pathogenic fungus ''[[Chondrostereum purpureum]]''.<ref name=Fry>{{cite book |author=Fry, William E.|title=Principles of Plant Disease Management |url=https://books.google.com/books?id=n1kxOTitCAgC&pg=PA187 |year=2012 |publisher=Academic Press |isbn=978-0-08-091830-3 |page=187}}</ref>

Pathogenic fungi may be controlled by other fungi, or bacteria or yeasts, such as: ''[[Gliocladium]]'' spp., [[mycoparasite|mycoparasitic]] ''[[Pythium]]'' spp., [[binucleate]] types of ''[[Rhizoctonia]]'' spp., and ''[[Laetisaria]]'' spp.

The fungi ''[[Cordyceps]]'' and ''[[Metacordyceps]]'' are deployed against a wide spectrum of arthropods.<ref>{{cite journal |author1=Santhosh, Kumar T. |author2=Aparna, N. S. |title=Cordyceps Species as a Bio-Control Agent against Coconut Root Grub, Leucopholis coneophora Burm |journal=Journal of Environmental Research and Development |volume=8 |issue=3A |date=2014 |pages=614–618 |url=https://www.jerad.org/ppapers/dnload.php?vl=8&is=3A&st=614 |access-date=2017-03-20 |archive-date=2018-10-04 |archive-url=https://web.archive.org/web/20181004085356/https://www.jerad.org/ppapers/dnload.php?vl=8&is=3A&st=614 |url-status=dead }}</ref> ''[[Entomophaga (fungus)|Entomophaga]]'' is effective against pests such as the [[Myzus persicae|green peach aphid]].<ref name=Capinera>{{cite web|url=http://entnemdept.ufl.edu/creatures/veg/aphid/green_peach_aphid.htm |title=Featured creatures: Peach Aphid |last=Capinera |first=John L. |date=October 2005 |website=University of Florida – Department of Entomology and Nematology |publisher=University of Florida |access-date=7 June 2016 |url-status=live |archive-url=https://web.archive.org/web/20160526234842/http://entnemdept.ufl.edu/creatures/veg/aphid/green_peach_aphid.htm |archive-date=26 May 2016 }}</ref>

Several members of [[Chytridiomycota]] and [[Blastocladiomycota]] have been explored as agents of biological control.<ref name=Li>{{cite journal | last1=Li | first1=Z. | last2=Dong | first2=Q. | last3=Albright | first3=T.P. | last4=Guo | first4=Q. | year=2011 | title=Natural and human dimensions of a quasi-natural wild species: the case of kudzu | journal=Biological Invasions | volume=13 | issue=10 | pages=2167–2179 | doi=10.1007/s10530-011-0042-7| s2cid=14948770 }}</ref><ref name=Frog>{{cite journal | last1 = Beard | first1 = Karen H. | last2 = O'Neill | first2 = Eric M. | year = 2005 | title = Infection of an invasive frog ''Eleutherodactylus coqui'' by the chytrid fungus ''Batrachochytrium dendrobatidis'' in Hawaii | doi = 10.1016/j.biocon.2005.07.004 | journal = Biological Conservation | volume = 126 | issue = 4| pages = 591–595 | bibcode = 2005BCons.126..591B | url = https://works.bepress.com/karenh_beard/106/download/ }}</ref><!--<ref name=Sparrow1960>{{cite book |author=Sparrow, F.K. |date=1960 |title=Aquatic Phycomyetes |publisher=University of Michigan Press |edition=2nd }}</ref>--> From Chytridiomycota, ''[[Synchytrium|Synchytrium solstitiale]]'' is being considered as a control agent of the [[Centaurea solstitialis|yellow star thistle]] (''Centaurea solstitialis'') in the United States.<ref name=Gleason>{{cite book |author1=Voigt K. |author2=Marano, A. V. |author3=Gleason, F. H.  |date=2013 |title=Ecological & Economical Importance of Parasitic Zoosporic True Fungi |work=The Mycota: A Comprehensive Treatise on Fungi as Experimental Systems for Basic & Applied Research Vol. 11 Agricultural Applications |edition=2nd |editor=K. Esser & F. Kempken |publisher=Springer |pages=243–270}}</ref>

====Viruses====
[[Baculoviridae|Baculoviruses]] are specific to individual insect host species and have been shown to be useful in [[Viral biological control|viral biological pest control]]. For example, the [[Lymantria dispar multicapsid nuclear polyhedrosis virus]] has been used to spray large areas of forest in North America where larvae of the [[Lymantria dispar dispar|spongy moth]] are causing serious defoliation. The moth larvae are killed by the virus they have eaten and die, the disintegrating cadavers leaving virus particles on the foliage to infect other larvae.<ref>{{cite web |author=D'Amico, Vince |url=https://biocontrol.entomology.cornell.edu/pathogens/baculoviruses.php |title=Biological control: Baculoviruses |publisher=Cornell University  |access-date=15 June 2016 |url-status=live |archive-url=https://web.archive.org/web/20160601063135/http://www.biocontrol.entomology.cornell.edu/pathogens/baculoviruses.php |archive-date=1 June 2016}}</ref>

A mammalian virus, the [[rabbit haemorrhagic disease virus]] was introduced to Australia to attempt to control the [[European rabbit]] populations there.<ref>{{cite journal|last1=Abrantes |first1=Joana |last2=van der Loo |first2=Wessel |last3=Le Pendu |first3=Jacques |last4=Esteves |first4=Pedro J. |title=Rabbit haemorrhagic disease (RHD) and rabbit haemorrhagic disease virus (RHDV): a review |journal=Veterinary Research |date=2012 |volume=43 |issue=12 |pages=12 |doi=10.1186/1297-9716-43-12 |pmid=22325049 |pmc=3331820 |doi-access=free }}</ref> It escaped from quarantine and spread across the country, killing large numbers of rabbits. Very young animals survived, passing immunity to their offspring in due course and eventually producing a virus-resistant population.<ref>{{cite web |url=http://www.csiro.au/Outcomes/Food-and-Agriculture/RCDFactsheet.aspx |format=pdf |title=Rabbit Calicivirus Disease (RCD) |last=Strive |first=Tanja |publisher=[[Commonwealth Scientific and Industrial Research Organisation]] |date=16 July 2008 |access-date=8 April 2017 |url-status=dead |archive-url=https://web.archive.org/web/20140415081441/http://www.csiro.au/Outcomes/Food-and-Agriculture/RCDFactsheet.aspx |archive-date=April 15, 2014 }}</ref> Introduction into New Zealand in the 1990s was similarly successful at first, but a decade later, immunity had developed and populations had returned to pre-RHD levels.<ref>{{cite news |title=Plan for 1080 drops in MacKenzie Basin |url=http://www.stuff.co.nz/the-press/news/2441711/Mackenzie-1080-drop-plan |last=Williams |first=David |date=26 May 2009 |newspaper=The Press |access-date=8 April 2017}}</ref>
{{further|Rabbits in Australia}}

RNA [[mycovirus]]es are controls of various fungal pathogens.<ref group="M" name="intro-examples-agents" />

==== Oomycota ====
''[[Lagenidium]] [[Lagenidium giganteum|giganteum]]'' is a water-borne mold that parasitizes the larval stage of mosquitoes. When applied to water, the motile spores avoid unsuitable host species and search out suitable mosquito larval hosts. This mold has the advantages of a dormant phase, resistant to desiccation, with slow-release characteristics over several years. Unfortunately, it is susceptible to many chemicals used in mosquito abatement programmes.<ref>{{cite web |url=https://biocontrol.entomology.cornell.edu/pathogens/lagenidium.php |title=Biological control: ''Lagenidium giganteum'' |author=Kerwin, James L. |publisher=Cornell University |access-date=15 June 2016 |url-status=dead |archive-date=20 June 2016 |archive-url=https://web.archive.org/web/20160620032211/http://www.biocontrol.entomology.cornell.edu/pathogens/lagenidium.php}}</ref>

===Competitors===
The [[legume]] vine ''[[Mucuna pruriens]]'' is used in the countries of [[Benin]] and [[Vietnam]] as a biological control for problematic ''[[Imperata cylindrica]]'' grass: the vine is extremely vigorous and suppresses neighbouring plants by [[Competition (biology)|out-competing]] them for space and light. ''Mucuna pruriens'' is said not to be invasive outside its cultivated area.<ref name="tropical">{{Cite web |url=http://www.tropicalforages.info/key/Forages/Media/Html/Mucuna_pruriens.htm |title=Factsheet – Mucuna pruriens |publisher=Tropical Forages |access-date=21 May 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080515210229/http://www.tropicalforages.info/key/Forages/Media/Html/Mucuna_pruriens.htm |archive-date=15 May 2008 }}</ref> ''[[Desmodium]] [[Desmodium uncinatum|uncinatum]]'' can be used in [[push-pull technology|push-pull farming]] to stop the [[parasitic plant]], witchweed (''[[Striga (plant)|Striga]]'').<ref>{{Cite journal | last1=Khan | first1=Z. | last2=Midega | first2=C. A. O. | last3=Amudavi | first3=D. M.  | last4=Hassanali | first4=A.| last5=Pickett | first5=J. A. | title=On-farm evaluation of the 'push–pull' technology for the control of stemborers and striga weed on maize in western Kenya| journal=Field Crops Research| volume=106| issue=3| pages=224–233| year=2008| doi=10.1016/j.fcr.2007.12.002| bibcode=2008FCrRe.106..224K }}</ref>

The Australian bush fly, ''[[Musca vetustissima]]'', is a major nuisance pest in Australia, but native decomposers found in Australia are not adapted to feeding on cow dung, which is where bush flies breed. Therefore, the [[Australian Dung Beetle Project]] (1965–1985), led by [[George Bornemissza]] of the [[Commonwealth Scientific and Industrial Research Organisation]], released forty-nine species of [[dung beetle]], to reduce the amount of dung and therefore also the potential breeding sites of the fly.<ref name="adbp">{{cite journal | last1=Bornemissza | first1=G. F. | year=1976 | title=The Australian dung beetle project 1965–1975 | journal=Australian Meat Research Committee Review | volume=30 | pages=1–30 }}</ref>

===Combined use of parasitoids and pathogens===

In cases of massive and severe infection of invasive pests, techniques of pest control are often used in combination. An example is the [[emerald ash borer]], ''[[Agrilus planipennis]]'', an invasive [[beetle]] from [[China]], which has destroyed tens of millions of [[ash trees]] in its introduced range in [[North America]]. As part of the campaign against it, from 2003 American scientists and the Chinese Academy of Forestry searched for its natural enemies in the wild, leading to the discovery of several parasitoid wasps, namely ''Tetrastichus planipennisi'', a gregarious larval endoparasitoid, ''[[Oobius agrili]]'', a solitary, parthenogenic egg parasitoid, and ''[[Spathius agrili]]'', a gregarious larval ectoparasitoid. These have been introduced and released into the [[United States|United States of America]] as a possible biological control of the emerald ash borer. Initial results for ''Tetrastichus planipennisi'' have shown promise, and it is now being released along with ''[[Beauveria bassiana]]'', a fungal [[pathogen]] with known insecticidal properties.<ref name="APHIS">{{Cite journal |last=Gould |first=Juli |author2=Bauer, Leah |title=Biological Control of Emerald Ash Borer (''Agrilus planipennis'') |url=http://www.aphis.usda.gov/plant_health/plant_pest_info/emerald_ash_b/downloads/eab-biocontrol.pdf |publisher=United States Department of Agriculture |access-date=28 April 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110110005023/http://www.aphis.usda.gov/plant_health/plant_pest_info/emerald_ash_b/downloads/eab-biocontrol.pdf |archive-date=10 January 2011 }}</ref><ref name="Bauer et al">{{cite journal|last1=Bauer |first1=L.S. |last2=Liu |first2=H.-P. |last3=Miller |first3=D. |last4=Gould |first4=J. |year=2008 |title=Developing a classical biological control program for Agrilus planipennis (Coleoptera: Buprestidae), an invasive ash pest in North America |journal=Newsletter of the Michigan Entomological Society |volume=53 |issue=3&4 |pages=38–39 |url=http://www.nrs.fs.fed.us/pubs/jrnl/2008/nrs_2008_bauer_002.pdf |access-date=29 April 2011 |url-status=live |archive-url=https://web.archive.org/web/20111004090830/http://www.nrs.fs.fed.us/pubs/jrnl/2008/nrs_2008_bauer_002.pdf |archive-date= 4 October 2011}}</ref><ref name="ScienceDaily">{{Cite web |url=https://www.sciencedaily.com/releases/2011/04/110426111415.htm |title=Biocontrol: Fungus and Wasps Released to Control Emerald Ash Borer |date=26 April 2011 |website=Science News |publisher=ScienceDaily |access-date=27 April 2011 |url-status=live |archive-url=https://web.archive.org/web/20110504012056/https://www.sciencedaily.com/releases/2011/04/110426111415.htm |archive-date=4 May 2011}}</ref>

=== Secondary plants ===

In addition, biological pest control sometimes makes use of plant defenses to reduce crop damage by herbivores. Techniques include [[polyculture]], the planting together of two or more species such as a primary crop and a secondary plant, which may also be a crop. This can allow the secondary plant's defensive chemicals to protect the crop planted with it.<ref name="Parolin Bresch 2012">{{cite journal | last1=Parolin | first1=Pia | last2=Bresch | first2=Cécile | last3=Desneux | first3=Nicolas | last4=Brun | first4=Richard | last5=Bout | first5=Alexandre | last6=Boll | first6=Roger | last7=Poncet | first7=Christine | title=Secondary plants used in biological control: A review | journal=International Journal of Pest Management | volume=58 | issue=2 | year=2012 | doi=10.1080/09670874.2012.659229 | pages=91–100}}</ref>

==Target pests==
===Fungal pests===
''[[Botrytis cinerea]]'' on [[lettuce]], by ''[[Fusarium]]'' spp. and ''[[Penicillium claviforme]]'', on [[grape]] and [[strawberry]] by ''[[Trichoderma]]'' spp., on strawberry by ''[[Cladosporium herbarum]]'', on [[Chinese cabbage]] by ''[[Bacillus brevis]]'', and on various other crops by various yeasts and bacteria. ''[[Sclerotinia sclerotiorum]]'' by several fungal biocontrols. Fungal pod infection of [[snap bean]] by ''[[Trichoderma hamatum]]'' if before or concurrent with infection.<ref group="M" name="intro-examples-pests">p.{{nbs}}93-4</ref> ''[[Cryphonectria parasitica]]'', ''[[Gaeumannomyces graminis]]'', ''[[Sclerotinia]]'' spp., and ''[[Ophiostoma novo-ulmi]]'' by viruses.<ref group="M" name="intro-examples-agents" /> Various [[powdery mildew]]s and [[rust (fungus)|rust]]s by various ''[[Bacillus]]'' spp. and [[fluorescent Pseudomonad]]s.<ref group="M" name="biocontrol-MoAs" /> ''[[Colletotrichum orbiculare]]'' will suppress further infection by itself if manipulated to produce [[plant-induced systemic resistance]] by infected the lowest leaf.<ref group="M" name="Induc-Res">p.{{nbs}}95-6</ref>

==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>

==Related techniques==
Related to biological pest control is the technique of introducing sterile individuals into the native population of some organism. This technique is widely practised with [[Sterile insect technique|insects]]: a large number of males sterilized by [[gamma radiation|radiation]] are released into the environment, which proceed to [[Competition (biology)|compete]] with the native males for females. Those females that copulate with the sterile males will lay infertile eggs, resulting in a decrease in the size of the population. Over time, with repeated introductions of sterile males, this could result in a significant decrease in the size of the organism's population.<ref>{{Cite book |last1=Robinson |first1=A. S.  |url=https://www.worldcat.org/oclc/1225257814 |title=Sterile Insect Technique: Principles and Practice in Area-Wide Integrated Pest Management |last2=Hendrichs |first2=J. |last3=Dyck |first3=V. A. |date=2021 |publisher=CRC Press |isbn=978-1-000-37776-7 |location=[S.l.] |oclc=1225257814}}</ref> A similar technique has recently been applied to weeds using irradiated pollen,<ref>{{cite patent| country = US| number = US20190208790A1| status = Pending| title = Compositions, kits and methods for weed control| pubdate = 2019-07-11| fdate = 2017-05-22| pridate = 2016-05-22| invent1 = Efrat Lidor-Nili| invent2 = Orly Noivirt-Brik| assign1 = Weedout Ltd.}}</ref> resulting in deformed seeds that do not sprout.<ref>{{Cite news |last=מורן |first=מירב |date=2020-12-30 |title=בלי כימיקלים: שתי מדעניות הגו רעיון פשוט ומהפכני לחיסול עשבים שוטים |language=he |work=הארץ |url=https://www.haaretz.co.il/magazine/.premium.HIGHLIGHT-MAGAZINE-1.9410439 |access-date=2021-01-05}}</ref>

==See also==
{{Div col}}
* [[Beneficial insects]]
* [[Chitosan]]
* [[Companion planting]]
* [[Insectary plants]]
* [[International Organization for Biological Control]]
* [[Inundative application]]
* [[Mating disruption]]
* [[Nematophagous fungus]]
* [[Organic gardening]]
* [[Organic farming]]
* [[Permaculture#Zones|Permaculture zone 5]]
* [[Sustainable farming]]
* [[Sustainable gardening]]
* [[Zero Budget Farming]]
* [[Entomovector]]
{{div col end}}

==References==
{{Reflist|refs=

<ref name="He-et-al-2021">{{cite journal | last1=He | first1=Xueqing | last2=Kiær | first2=Lars Pødenphant | last3=Jensen | first3=Per Moestrup | last4=Sigsgaard | first4=Lene | title=The effect of floral resources on predator longevity and fecundity: A systematic review and meta-analysis | journal=[[Biological Control (journal)|Biological Control]] | publisher=[[Elsevier]] BV | volume=153 | year=2021 | issn=1049-9644 | doi=10.1016/j.biocontrol.2020.104476 | page=104476| bibcode=2021BiolC.15304476H | s2cid=228829546 }}</ref>

<ref name="He-Sigsgaard-2019">{{cite journal | last1=He | first1=Xueqing | last2=Sigsgaard | first2=Lene | title=A Floral Diet Increases the Longevity of the Coccinellid ''Adalia bipunctata'' but Does Not Allow Molting or Reproduction | journal=[[Frontiers in Ecology and Evolution]] | publisher=[[Frontiers Media]] SA | volume=7 | date=2019-02-05 | page=6 | issn=2296-701X | doi=10.3389/fevo.2019.00006| doi-access=free | bibcode=2019FrEEv...7....6H }}</ref>

}}
* {{cite book | editor=K. Esser and J.W. Bennett | series=The Mycota - A Comprehensive Treatise on Fungi as Experimental Systems for Basic and Applied Research | title=XI Agricultural Applications | publisher=Springer Berlin Heidelberg | publication-place=Berlin, Heidelberg | year=2002 | isbn=978-3-662-03059-2 | oclc=851379901 | page=VII-388 }} {{isbn|978-3-642-07650-3}}
:*Chapter 6, {{cite book | last1=Elad | first1=Yigal | last2=Freeman | first2=Stanley | chapter=Biological Control of Fungal Plant Pathogens | title={{nbs}}}}
{{reflist | group="M"}}

== Further reading ==
===General===
* Wiedenmann, R. (2000). [http://www.inhs.uiuc.edu/research/biocontrol Introduction to Biological Control] {{Webarchive|url=https://web.archive.org/web/20110810071903/http://www.inhs.uiuc.edu/research/biocontrol/ |date=2011-08-10 }}. Midwest Institute for Biological Control, Illinois.
* {{cite journal | last1=Cowie | first1=R. H. | year=2001 | title=Can snails ever be effective and safe biocontrol agents? | url=http://www.institutohorus.org.br/download/artigos/Cowie%202001.pdf | journal=International Journal of Pest Management | volume=47 | issue=1 | pages=23–40 | doi=10.1080/09670870150215577 | citeseerx=10.1.1.694.2798 | s2cid=51510769 | access-date=2010-04-07 | archive-url=https://web.archive.org/web/20101011210953/http://www.institutohorus.org.br/download/artigos/Cowie%202001.pdf | archive-date=2010-10-11 | url-status=dead }}
* {{cite journal | author=Cook, R. James | journal=Annual Review of Phytopathology |date=September 1993 | volume=31 | pages=53–80 | title=Making Greater Use of Introduced Microorganisms for Biological Control of Plant Pathogens | doi=10.1146/annurev.py.31.090193.000413 | pmid=18643761 | issue=1| bibcode=1993AnRvP..31...53C }}
* {{cite journal | author=U.S. Congress, Office of Technology Assessment | year=1995 | title=Biologically based technologies for pest control | journal=Ota-Env-636 | url=http://www.princeton.edu/~ota/disk1/1995/9506/9506.PDF}}
* {{Cite book| author=Felix Wäckers | author2=Paul van Rijn | author3=Jan Bruin | name-list-style=amp| publisher=Cambridge University Press, 2005 | year=2005 | title=Plant-Provided Food for Carnivorous Insects – a protective mutualism and its applications | isbn=978-0-521-81941-1}}

===Effects on native biodiversity===
* {{cite journal | last1 = Pereira | first1 = M. J. | display-authors = etal | year = 1998 | title = Conservation of natural vegetation in Azores Islands | journal = Bol. Mus. Munic. Funchal | volume = 5 | pages = 299–305 }}
* Weeden, C. R.; Shelton, A. M.; Hoffman, M. P. [https://web.archive.org/web/20071026104009/http://www.nysaes.cornell.edu/ent/biocontrol/predators/rodolia_cardinalis.html Biological Control: A Guide to Natural Enemies in North America].
* [https://web.archive.org/web/20071123044914/http://www.biotechnologyonline.gov.au/enviro/canetoad.cfm Cane toad: a case study]. 2003.
* Humphrey, J. and Hyatt. 2004. CSIRO Australian Animal Health Laboratory. ''Biological Control of the Cane Toad Bufo marinus in Australia''
* {{cite journal | last1=Cory | first1=J. | last2=Myers | first2=J. | year=2000 | title=Direct and indirect ecological effects of biological control | journal=Trends in Ecology & Evolution | volume=15 | issue=4| pages=137–139 | doi=10.1016/s0169-5347(99)01807-8| bibcode=2000TEcoE..15..137C }}
* Johnson, M. 2000. Nature and Scope of Biological Control. ''Biological Control of Pests''.

===Economic effects===
* {{cite journal | last1 = Griffiths | first1 = G. J. K. | year = 2007 | title = Efficacy and economics of shelter habitats for conservation | journal = Biological Control | volume =  45| pages =  200–209| doi = 10.1016/j.biocontrol.2007.09.002 }}
* {{cite journal | last1 = Collier | first1 = T. | last2 = Steenwyka | first2 = R. | year = 2003 | title = A critical evaluation of augmentative biological control | journal = Economics of Augmentation | volume = 31 | issue = 2| pages = 245–256 | doi = 10.1016/j.biocontrol.2004.05.001 }}

==External links==
{{Commons category|Biological pest control agents}}
* [http://www.anbp.org Association of Natural Biocontrol Producers]
* [http://www.iobc-global.org/ International Organization for Biological Control]

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