Editing Western corn rootworm (section)

== Management ==
Multiple management practices aim to control corn rootworms. These practices include corn variety selection, early planting, [[insecticides]], [[crop rotation]] and [[transgenic]] corn varieties.{{Cn|date=January 2021}}

=== Variety ===
No commercial, non-transgenic resistant corn varieties are available. Several [[hybrid corn]] traits reduce damage by increasing stalk strength and root mass size. These characteristics allow a plant to better tolerate rootworm feeding, with reduced likelihood of lodging.<ref name="Wright" />

=== Early planting ===
Early planted fields that have completed pollen shed are less attractive and therefore have less egg laying activity. Early fields have relatively larger root systems when rootworm feeding starts. This makes them somewhat more tolerant. Practices that promote strong root systems and a generally vigorous crop make corn more tolerant to rootworm feeding and damage.<ref name=peairs>Peairs, F. B. and S. D. Pilcher. [http://www.ext.colostate.edu/PUBS/insect/05570.html Western Corn Rootworm] Colorado State University. March 24, 2006. Viewed February 3, 2007</ref>

=== Insecticides ===
Soil-applied [[insecticide]]s effectively control corn rootworms. Insecticide may be warranted in areas that have a history of moderate to high damage. The number of adults present during the previous growing season is the best guide for selecting fields to be treated.<ref name=peairs/> However, in some areas of high insecticide use in central [[Nebraska]], populations of corn rootworm beetles have become resistant to certain insecticides. [[Aldrin]] resistance was probably introduced independently, at least twice, from North America into Europe. [[Organophosphate]]s, such as [[methyl-parathion]], may provide effective control of both larval and adult populations in Central and southeastern Europe and in northwest Italy.<ref name="Ciosi_2009">{{Cite journal | doi = 10.1111/j.1439-0418.2008.01363.x| title = European populations of ''Diabrotica'' virgifera virgiferaare resistant to aldrin, but not to methyl-parathion| journal = Journal of Applied Entomology| volume = 133| issue = 4| pages = 307–314| year = 2009| last1 = Ciosi| first1 = M.| last2 = Toepfer| first2 = S.| last3 = Li| first3 = H.| last4 = Haye| first4 = T.| last5 = Kuhlmann| first5 = U.| last6 = Wang| first6 = H.| last7 = Siegfried| first7 = B.| last8 = Guillemaud| first8 = T.| s2cid = 10040670| url = http://eprints.gla.ac.uk/60358/1/60358.pdf}}</ref>

=== Crop rotation ===
[[Crop rotation]] is a consistent and economical means of controlling rootworms the season following an outbreak in corn-growing areas where rootworm beetles primarily lay eggs in corn. As a way to reduce rootworm densities, it is more effective than insecticides.<ref name=Wright/> Corn rootworm larvae must feed on corn roots to develop and mature properly. If they hatch in a field without corn, they starve because they cannot move more than 10 to {{convert|20|in|mm}} in search of food.<ref name=peairs/> However, two rootworm biotypes survive rotation. The "soybean" variant was first discovered in central Illinois in the late 1980s and spread throughout Illinois, Indiana, southern Wisconsin and eastern Iowa.<ref>Rice, M. E. and J. J. Tollefson. [http://www.ipm.iastate.edu/ipm/icm/2006/3-13/variant.html The variant western corn rootworm in Iowa. Iowa State University]. March 13, 2006. Viewed February 3, 2007.</ref> Instead of laying eggs into a corn field, the females of the soybean variant mate and then fly into a soybean field to lay their eggs, allowing the larvae to hatch in a field likely to rotate back to corn the following year. In the 1980s northern corn rootworm began to be a problem by beating the corn rotation practice with extended [[diapause]] eggs.<ref>Willson H. R. and J. B. Eisley. [http://ohioline.osu.edu/ent-fact/0017.html Monitoring Western Corn Rootworm Activity in Soybeans to Predict Rootworm Injury in First-Year Corn]. August 2001. Viewed February 3, 2007.</ref> The eggs remained in the soil for two years or more before hatching, thereby avoiding the soybean year. As of 2017, this adaptation has been observed in areas of Iowa, Minnesota and South Dakota, Wisconsin and Nebraska.<ref>{{Cite journal|last1=Calles-Torrez|first1=Veronica|last2=Knodel|first2=Janet J|last3=Boetel|first3=Mark A|last4=French|first4=B Wade|last5=Fuller|first5=Billy W|last6=Ransom|first6=Joel K|date=2019-05-22|title=Field-Evolved Resistance of Northern and Western Corn Rootworm (Coleoptera: Chrysomelidae) Populations to Corn Hybrids Expressing Single and Pyramided Cry3Bb1 and Cry34/35Ab1 Bt Proteins in North Dakota|journal=Journal of Economic Entomology|volume=112|issue=4|pages=1875–1886|doi=10.1093/jee/toz111|pmid=31114868|s2cid=162170836|issn=0022-0493}}</ref>

Companion or second crop planting can dramatically increase rootworm populations. Corn with pumpkins or corn following pumpkins are examples of planting patterns that exacerbate rootworm feeding pressure.<ref>{{Cite journal|last1=Grozea|first1=Ioana|last2=Stef|first2=Ramona|last3=Virteiu|first3=Ana Maria|last4=Molnar|first4=Levente|last5=Carabet|first5=Alin|last6=Puia|first6=Carmen|last7=Dobrin|first7=Ionela|date=2015-11-27|title=Feeding behaviour of Diabrotica virgifera virgifera adults on corn crops|journal=Bulletin of University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca. Horticulture|volume=72|issue=2|doi=10.15835/buasvmcn-hort:11393|issn=1843-5394|doi-access=free}}</ref>

Shrestha, Dunbar, French and Gassmann have reported that field history causes variation in the degree of corn rootworm resistance. All the fields they found had corn rootworms resistant to the traits, but they observed that significantly more corn rootworm larvae survived in fields with Bt resistance. They recommend faithful crop rotation not only for reducing the population of the worm, but to slow the adaptation of the worm as well.<ref>{{Cite journal|last1=Shrestha|first1=Ram B.|last2=Dunbar|first2=Mike W.|last3=French|first3=Bryan W.|last4=Gassmann|first4=Aaron J.|date=2018-07-03|title=Effects of field history on resistance to Bt maize by western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae)|journal=PLOS ONE|language=en|volume=13|issue=7|pages=e0200156|doi=10.1371/journal.pone.0200156|issn=1932-6203|pmc=6029802|pmid=29969492|bibcode=2018PLoSO..1300156S|doi-access=free}}</ref>

=== Natural enemies ===
Among natural enemies - [[Argiope bruennichi]], Theridion impressum, [[Coccinella]] sp., Pseudophomus rufipes.<ref>{{cite journal| pmid=19226790 | volume=73 | issue=3 | title=Natural enemies in control of invasive species Diabrotica virgifera Virgifera from maize crops | year=2008 | journal=Commun Agric Appl Biol Sci | pages=501–8 | last1 = Grozea | first1 = I | last2 = Carabet | first2 = A | last3 = Chirita | first3 = R | last4 = Badea | first4 = AM}}</ref>

=== Transgenics ===
Planting rootworm-resistant transgenic corn is another strategy for minimizing damage.<ref>{{cite journal|last=Devos|first=Yann|author2=Lisa N. Meihls |author3=Jószef Kiss |author4=Bruce E. Hibbard |title=Resistance evolution to the first generation of genetically modified Diabrotica-active Bt-maize events by western corn rootworm: management and monitoring considerations|journal=Transgenic Research|year=2013|volume=22|issue=2|pages=269–299|pmid=23011587|doi=10.1007/s11248-012-9657-4|s2cid=10821353|url=https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=2247&context=usdaarsfacpub|url-access=subscription}}</ref> [[Bt corn]] is effective at reducing root damage and is safer and often cheaper than insecticide. The transgenic traits, isolated from the common soil [[bacterium]] ''[[Bacillus thuringiensis]]'' strain (often referred to as Bt), produce the insect control protein.{{Cn|date=January 2021}}

Bt was first discovered in 1901 by Japanese biologist S. Ishiwatari as the source of disease that was killing large populations of [[silkworm]]s. Bt was first used as an insecticide in 1920 and spray formulations containing either Bt bacteria or Bt proteins came into use in the 1970s for [[crop protection]], including [[organic farming]] operations. Bt insecticides saw expanded use and development in the 1980s as an alternative to synthetic insecticides. Beginning in the 1980s, the genes responsible for making ''Bt'' proteins were isolated and transferred into corn plants. Bt was commercially approved in transgenic corn seed in the mid-1990s. Compared to spray formulations, transgenic plants with the Bt protein provide much more effective insect protection throughout the season. Other Bt proteins have been used to genetically modify potatoes, cotton and other types of commercial corn. The two most common brands of transgenic Bt corn are [[Genuity (Monsanto brand)|Genuity]] and [[Herculex]].{{Citation needed|date=July 2010}} [[Genuity Smartstax]] combines [[Monsanto]]'s [[VT Triple Pro]], [[Roundup (herbicide)|Roundup]] Ready 2, and [[Acceleron Seed Treatment System]] technologies, as well as [[Dow Chemical]]'s Herculex Xtra and [[Liberty Link]] technologies. Acceleron, Herculex Xtra, and VT Triple Pro include traits for protection from insect damage.{{Cn|date=January 2021}}

Bt must be ingested to kill the insect. A susceptible larva eats the protein, which then binds to receptors in the larval gut. Binding initiates a cascade of effects that ultimately leads to death. Bt proteins are highly selective on certain categories and species of insects, eliminating insecticide use and its harmful effects to non-target organisms.<ref>The Dow Chemical Company. [http://www.dow.com/productsafety/finder/herculex.htm Product Safety Assessment (PSA): Herculex RW Rootworm Protection]. September 26, 2006. Viewed February 3, 2007.</ref>

Recently, however, strains of rootworms that exhibit Bt resistance have been discovered in several Midwestern US states.<ref name="DOI10.1371/journal.pone.0022629">{{Cite journal | doi = 10.1371/journal.pone.0022629| pmid = 21829470| title = Field-Evolved Resistance to Bt Maize by Western Corn Rootworm| journal = PLOS ONE| volume = 6| issue = 7| pages = e22629| year = 2011| last1 = Gassmann | first1 = A. J. | last2 = Petzold-Maxwell | first2 = J. L. | last3 = Keweshan | first3 = R. S. | last4 = Dunbar | first4 = M. W. | pmc=3146474| bibcode = 2011PLoSO...622629G| doi-access = free}}</ref> According to Monsanto, the "YieldGard VT Triple and Genuity VT Triple PRO corn products" are affected. In 2009, four strains in Iowa were found to have field-evolved resistance to Bt corn.<ref>{{cite journal|last=Gassman|first=Aaron J|title=Field-evolved resistance to Bt maize by western corn rootworm: Predictions from the laboratory and effects in the field|journal=Journal of Invertebrate Pathology|date=July 2012|volume=110|issue=3|pages=287–293|pmid=22537837|doi=10.1016/j.jip.2012.04.006|bibcode=2012JInvP.110..287G }}</ref> Some rootworms were found to be resistant to two or more Bt toxins in addition to being tolerant to crop rotation. This ability to rapidly evolve to adapt to multiple traits in their new food source has proved to be a challenge for farmers and scientists. That same year, Monsanto, DuPont Pioneer, Syngenta and Dow Agro-Sciences all began to sell "stacked" or pyramid corn seed designed to slow the development of resistance. These products combined traits to increase effectiveness, however, so many of these traits are failing that soon they will run out of ingredients to stack. A new bacterial gene has been discovered by researchers that will kill rootworms, but it is not expected to be available to farmers before 2029.<ref>{{Cite journal|last=Nordhaus|first=Hannah|date=2017-02-14|title=Cornboy vs. the Billion-Dollar Bug|journal=Scientific American|volume=316|issue=3|pages=64–71|doi=10.1038/scientificamerican0317-64|pmid=28207712|issn=0036-8733|bibcode=2017SciAm.316c..64N}}</ref>

By 2014 [[Syngenta]] Agrisure RW-rootworm strains had been detected in Iowa as well as [[glyphosate]]. Agrisure RW-based products entered the market in 2007. However, government officials, academics and companies lack consensus on how to define the resistance phenomenon. The affected fields constituted 0.2% of transgenic US corn acres. Further the affected areas had not been rotated with other crops.<ref name=wsj1402>{{cite news|last=Bunge |first=Jacob |url=https://online.wsj.com/news/articles/SB10001424052702304157204579475782097509254?mg=reno64-wsj |title=Farm Belt Pest Gnaws at Syngenta |access-date=2014-04-04|newspaper=Wall Street Journal |date=April 1, 2014 }}</ref>

As of December 2018, the corn rootworm has been found to be resistant to all four traits.<ref>{{Cite web|last=Gullickson|first=Gil|url=https://www.agriculture.com/crops/corn/why-managing-corn-rootworm-just-became-more-complicated|title=Why Managing Corn Rootworm Just Became More Complicated|date=December 1, 2018|website=Successful Farming|archive-url=|archive-date=|access-date=}}</ref>

=== Biological solutions ===
In Austria, an innovative protection method has been developed, using the "mating disruption" method for the first time in corn fields. The according product is called CornProtect.<ref>{{Cite web | url=http://www.lithosnatural.at/en/cornprotect | title=Lithos natural &#124; CornProtect}}</ref> The female bugs distribute pheromones that attract males. With that new method, such pheromones are put on specially treated mineral carriers and are slowly released over the full flying period of the bugs. Mating is significantly reduced, because males become disoriented and less interested in copulating. Reproduction is drastically reduced <ref>{{Cite web | url=https://www.landwirt.com/Maiswurzelbohrer-verwirren,,14319,,Bericht.html | title=Maiswurzelbohrer verwirren}}</ref> The application is done with conventional field sprayers which makes it economically very viable.<ref>{{Cite web | url=https://www.topagrar.at/ackerbau/Mit-Pheromonen-gegen-den-Maiswurzelbohrer-1885545.html | title=Mit Pheromonen gegen den Maiswurzelbohrer| date=2019-02-04}}</ref>