Editing Biological pest control (section)

===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>