Editing Scale insect (section)

===As pests===

Many scale species are serious crop [[pest (animal)|pest]]s and are particularly problematic for their ability to evade [[Pest quarantine|quarantine]] measures.<ref>{{Cite journal |last1=Sethusa |first1=M.T. |last2=Millar |first2=I.M. |last3=Yessoufou |first3=K. |last4=Jacobs |first4=A. |last5=Bank |first5=M. van der |last6=Bank |first6=H. van der |date=2014 |title=DNA Barcode Efficacy for the Identification of Economically Important Scale Insects (Hemiptera: Coccoidea) in South Africa |url=http://www.bioone.org/doi/abs/10.4001/003.022.0218 |journal=African Entomology |language=en |volume=22 |issue=2 |pages=257–266 |doi=10.4001/003.022.0218 |s2cid=84171305 |issn=1021-3589|url-access=subscription }}</ref><ref name="ISU">{{cite web |title=Scale Insects |url=https://hortnews.extension.iastate.edu/scale-insects |publisher=Iowa State University |access-date=14 January 2020}}</ref> In 1990, they caused around $5&nbsp;billion of damage to crops in the United States.<ref name="Piper2011">{{cite book |last=Piper |first=Ross |title=Pests: A Guide to the World's Most Maligned, Yet Misunderstood Creatures |url=https://books.google.com/books?id=wRDIOhoQR68C&pg=PA149 |year=2011 |publisher=ABC-CLIO |isbn=978-0-313-38426-4 |page=149}}</ref>
The waxy covering of many species of scale protects their adults effectively from contact [[insecticide]]s, which are only effective against the first-instar [[Nymph (biology)|nymph]] stage known as the ''crawler''. However, scales can often be controlled using [[horticultural oil]]s that [[suffocation|suffocate]] them, systemic pesticides that poison the sap of the host plants, or by [[biological control]] agents such as tiny [[parasitoid]] wasps and ladybirds. [[Insecticidal soap]] may also be used against scales.<ref>{{cite web |title=Scale insects |url=https://www.gardenersworld.com/how-to/solve-problems/scale-insects/ |website=[[Gardeners' World]] |access-date=16 January 2020}}</ref>

One species, the cottony cushion scale, is a serious commercial pest on 65 families of woody plants, including ''[[Citrus]]'' fruits. It has spread worldwide from Australia.<ref>[http://scalenet.info/catalogue/Icerya%20purchasi/ ScaleNet]</ref><ref>{{cite book |last=Nair |first=K. S. S. |date=2007 |title=Tropical Forest Insect Pests: Ecology, Impact, and Management |url=https://books.google.com/books?id=QvOPufXCJq0C&pg=PA221 |publisher=Cambridge University Press |isbn=9781139464857 |page=221}}</ref>

<gallery class="center" mode="nolines" widths="200px" heights="200px">
File:Icerya purchasi feeding on Citrus.jpg|Adult female [[cottony cushion scale]] (''Icerya purchasi'') with young crawlers. The species is a major commercial pest of crops such as ''Citrus'' fruits.
File:Anagyrus lopezi.jpg|The tiny [[parasitic wasp]] ''[[Anagyrus|Anagyrus lopezi]]'', a highly effective biological control of the [[cassava]] mealybug
</gallery>