Western corn rootworm

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Western corn rootworm
Western corn rootworm (Diabrotica virgifera)

Western corn rootworm ( Diabrotica virgifera )

Systematics
Order : Beetle (Coleoptera)
Subordination : Polyphaga
Family : Leaf beetles (Chrysomelidae)
Subfamily : Galerucinae
Genre : Diabrotica
Type : Western corn rootworm
Scientific name
Diabrotica virgifera
LeConte , 1858
Western corn rootworm

The western corn rootworm ( Diabrotica virgifera ) is a species of beetle from the leaf beetle family (Chrysomelidae). It was originally located in Central America and quickly spread as the so-called Western Corn Rootworm in the USA and Canada in the cultivation of maize. It has also been naturalized in Europe since the beginning of the 1990s and is also increasingly damaging corn-growing areas.

features

The corn rootworm is about 5 mm long and has a yellow-black color and characteristic antennae, which often span the body. The abdomen and legs are yellow. Chavicol is an attractant for him.

Host plants

The main food of the beetle larvae is maize ( Zea mays ). In addition, the beetle feeds itself on pollen from Amaranthus sp., Chenopodium album ( white goose foot ), Ambrosia artemisiifolia (sagebrush ragweed), Xanthium strumarium (common burdock) and Helianthus annuus (sunflower) as well as various curcubitaceans (pumpkin, melon, cucumber, Zucchini), soybean and alfalfa. In 2001, for example, the beetles were detected in pheromone traps placed between soy , sunflowers and grain (J. Moeser, S. Vidal, Department of Crop Science, Georg-August-Universität Göttingen ).

origin

The species is native to Central America (Guatemala, Nicaragua, Costa Rica). The first sighting took place in Kansas in 1867 on a wild pumpkin ( Cucurbita foetidissima ). From there the beetle spread to the granaries in the north. Until 1909 it only appeared east of the Rocky Mountains, but over the years it spread to the east coast. Since 1955, the corn rootworm has progressively infested all major corn cultivation areas in the USA and Canada ( Ontario ), making the beetle the most important corn pest.

Infested areas in Europe

Starting from his original area of ​​origin, he moved to Europe in 1992. It was first detected near Paris in 2002, but the corn rootworm has now spread across Europe. Genetic analyzes have shown that the beetles occurring in Europe are descendants from at least three different populations and are thus introductory events.

Strong affected

Yugoslavia (1998), Croatia (1995), Bosnia-Herzegovina (1997), Hungary (1992)

Expanding

Romania (1996), Bulgaria (1998), Slovakia (2000), Ukraine (2001), Italy (1998), Czech Republic (2002), Austria (2002), Slovenia (2003), Poland (2010)

Occasional phenomena

In the meantime, further infested fields were found in Italy (1998), Switzerland (2000), France (2002), Serbia (1992), Montenegro (1998), Belgium (2003), the Netherlands (2005) and Great Britain (2003). The beetle was first detected in Germany in 2007 in the Ortenau district . The corn rootworm was first observed in Upper Austria at the beginning of August 2007. From there it spread to Germany in the Inn and Danube valleys. Since August 14, 2007, over 100 beetles have been detected near Passau . The pest appeared in the Lake Constance area at the end of August 2007. The source of infestation is near Salem between Frickingen and Altheim. On September 5, 2011, the Rhineland-Palatinate plant protection service caught a beetle in an attractant trap for the first time in the Bodenheim district. In August 2012, two beetles were caught in the southern Palatinate.

Damage reports

In Lombardy , at least 30% of the harvest was destroyed in 2009 (corresponding to 1 million tons). The affected Po Valley was officially classified as a disaster area, quarantine measures were ordered in accordance with EU regulations and a two-year cultivation ban was imposed.

Spread

Naturally

The beetles spread naturally by flight. The flight time ranges from July to October. A single flight can cover up to 25 kilometers. The heavily infested areas are expanded by 40 to 80 kilometers every year. According to current estimates, the natural spread in Europe can no longer be stopped, only delayed. It is to be feared that the spread of the beetle in Europe will in the long term have similar consequences for maize cultivation as in the USA.

Procrastination

The corn rootworm is an example of an invasive species , i.e. animals or plants that have been moved by humans to areas where they were not originally found. Carryover via means of transport such as air, rail, ship and car plays an important role in this. It is assumed that the beetle reached Europe from the American continent by plane. The first infestation in 1992 near the Belgrade airport supports this theory of the entomologist Baca Franja. At that time, planes with aid supplies from the USA landed there because of the then raging Balkan War. The fact that some of the countries affected in Europe are not neighboring also indicates the spread of the beetles via modern means of transport.

Symptoms

Infested maize plants can be easily pulled out of the ground because the root system is no longer intact. A system of tubes in the root system is a typical symptom of the infestation. Even the goose neck ( goose-necking ) is considered as an indication.

IOWA scale

The University of Iowa developed a so-called scale to classify the damage. This is now only made up of three parts, but the original six-part variant for determining the damage caused by the larvae of the corn rootworm is still in use in Europe:

  • 1.0 without root corrosion
  • 1.5 some traces of feeding
  • 2.0 a maximum of three roots slightly gnawed
  • 2.5 slightly gnawed more than three roots, but none to within four centimeters of the stem
  • 3.0 a maximum of three roots gnawed under four centimeters from the stem
  • 3.5 more than three roots gnawed under four centimeters from the stem
  • 4.0 gnawed a whole root ring
  • 4.5 1.5 root rings
  • 5.0 2 root rings
  • 5.5 2.5 root rings
  • 6.0 more than three root rings completely destroyed

Damage threshold

According to the scale of the damage threshold in crop production, an infestation of 0.6 beetles per plant is sufficient for the beetle population to cause economic damage.

Injuries

Damage occurs both (mainly) by the larvae and by the beetles, which alternate in their temporal occurrence. The larvae specialize in maize and related sweet grasses ( Poaceae ), but the adult beetles are far more adaptable to food plants. The full extent of the damage is found around five years after the initial attack.

Larvae

In late summer, after mating (after two weeks of ripening ), the females lay about 500 eggs (0.5 millimeters in diameter) near a maize plant. However, the young larvae can also feed on grasses (millet, millet, and millet) and grain (wheat). The eggs released in August overwinter in the soil at a depth of 10 to 30 centimeters. The drier the soil, the deeper the eggs can be found. About five percent of the eggs are found outside of corn fields. These develop by May of the next year, if the soil temperature does not drop below minus ten degrees. Some eggs survive a year - so they survive two winter periods. The slip occurs larvae - tuned to the local temperature conditions - to July. The larvae develop in three stages, each separated by a molt, and mature into beetles in 40 days:

First stage

The hatched larvae can migrate up to a meter and then fall over the main and aerial roots of the maize plant. In the event of severe infestation, the plant dies because the damaged root system can no longer meet the water and nutrient requirements of the above-ground parts of the plant.

Second stage

Older larvae eat their way to the root heart in the second larval stage and thus damage the plant directly. The name corn rootworm suggests that the larvae literally drill their way into the root system and leave a typical tube system in the infected root. If the entire root system has been eaten away, one speaks of "root pruning". In the absence of support from the destroyed roots, the plants often tip over in a light wind ( storage ); in the case of severe infestation, this can affect three quarters of the cultivated area. Plants that have fallen over but not damaged too much straighten up again and then show crooked growth, the so-called goose neck . In this state, conventional agricultural machines can no longer harvest the corn correctly.

The eating also leads to fungal infections of the plant.

Third stage

After the eating phase on the maize plant, the larvae pupate in the ground for a week. After the third larval stage, the adult beetles, capable of flight, hatch from the approximately four millimeter long pupae. They usually mate on the first day and can be found until late autumn, i.e. until the frost breaks.

Beetle

The adult beetles particularly prefer stigmas (the soft "hairs" on the cob) of the female inflorescences (silk clipping on the inflorescences ) and the pollen as food . In addition to the damage to the scar threads, they also infect milk-ripe maize kernels (damage to the young, soft, i.e. juicy maize kernels). If the plants have not yet developed flower organs, the young leaves of the maize plant will eat windows. Heavy damage to the scar threads has an impact on the fertilization of the affected plant. The damaged corn plant hardly forms any more grains on the corn cob. Often times, the remaining grains take on unnatural shapes from subsequent fungal infections. This usually leads to a loss of a third of the yield.

The beetles do not disdain pollen from other plant species either. They also switch to daisy family (Asteraceae), legumes ( Fabaceae ) and cucurbits ( Cucurbitaceae ).

Injuries

In Austria, the loss of earnings is estimated at up to € 75 million. Globally, it is estimated that 20 million hectares of maize are infested with the corn rootworm and treated with insecticides (Fuller et al. 1997). 14 million hectares alone - and thus annual losses of around US $ 1 billion - are in the USA (MetCalf, 1986). That is why the pest also bears the title "One Billion Dollar Beetle". An average of ten percent of the harvest on infested areas is lost. In individual cases, however, the rate is up to 90 percent, for example in Serbia and Hungary. Should the beetle penetrate more strongly into Germany, a quarter of the 1.5 million hectares of maize areas would be acutely threatened, according to the Federal Biological Institute for Agriculture and Forestry. The EU currently estimates the damage to be expected at half a billion euros.

Combat

The corn rootworm has no natural enemies in Europe. Crop rotation management has the most sustainable effect if it does not cultivate maize for at least three years. In contrast, provide insecticide applications as another option a sensitive intervention in the ecology of the corn shocks affected are and can in Habitat located food chains severely damage.

By crop rotation

The pest spreads particularly on monocultures and is relatively easy to contain by adhering to the crop rotation. The alternating crops, i.e. the cultivation of maize only every three years, naturally deprives the larvae and beetles of food. Due to a lack of ability to migrate, the larvae of the previous year starve to death after hatching because they cannot find the host plants that they need for their development. In Austria, it was found that by adhering to a crop rotation with a low proportion of maize, the spread of the pest could be contained to 15 kilometers per year. In Switzerland, the infestation was successfully eliminated through crop rotation effects. Monocot subsequent crops, such as cereals, can, however, serve as food for the beetle. That is why dicotyledonous crop rotations are preferable.

Disadvantages of a two-year crop rotation: From 1960 to 1990, the crop rotation of corn on soy was successful in the USA. But this resulted in such great selection pressure that a new, rotation- tolerant biotype of Diabrotica was created, whose females also laid their eggs in soy fields, so that the larvae found maize plants as a source of food.

Chemically

By spraying

Insecticides can be used in growing areas without crop rotation. Since maize grows to about two meters, it is difficult to spray the usable areas in order to allow fertilization or to contain the infestation in the following year. In the USA, airplanes and helicopters are used. It is also possible to take action against the beetles with stilt tractors or normal tractors with the spray boom raised. Because of these difficulties, the preventive dressing of the seeds is probably the least expensive. After dressing, there is no need to spray the leaves under the leaves, which means that insecticidal applications of the leaves of the cultivated plant at an early stage are not necessary.

According to the Austrian Agency for Health and Food Safety (AGES), chemical applications in the USA have an efficiency of 60 to 80%, in Europe it is 60 to 90%. Corn rootworms that are resistant to the active ingredients parathion-methyl (ME 605) and carbaryl can now be found in Nebraska .

Worldwide, around 5,000 tons of active ingredients are used against the corn rootworm on 5 million hectares.

During the first sighting in Alsace, several helicopters sprayed 1.5 tons of the pyrethroid Lambda- Cyhalothrin (Karate Zeon).

Systemically acting neonicotinoids such as clothianidin (poncho) are also used. The funds are available as granules or in liquid form. The seedling and the young plant absorb the defense substance via the roots and integrate it into their tissue. Systemic means that the active ingredient is evenly distributed even on untreated tissue areas or parts of the plant that have grown on. The sucking and eating pest immediately interrupts further food intake after contact with the active ingredient.

Dressing the seeds

Agro companies like Bayer CropScience now recommending, all seeds with clothianidin to pickling to prevent to an infestation by the larvae. The drug was approved in North America in 2003, and in 2005 it was also approved in Germany. In Austria, the dressing of maize seeds with clothianidin has been mandatory since 2005.

In May / June 2008 in the Rhine Valley, when maize dressed with clothianidin was sown, massive bee deaths occurred, which was demonstrably due to this active ingredient. According to the manufacturer, the reason for this was incorrect handling of some seed batches. In connection with certain seed drills, extreme drought and strong winds, this had led to increased dust abrasion. As a result, the approval for all seed dressings with the active ingredient clothianidin was suspended. Only a few weeks later, however, the products were re-approved for certain uses, for example when sowing winter rape.

With messenger substances (semiochemicals)

The USA is currently working on a messenger substance , i.e. a natural connection that changes the behavior of an animal. Here are used cucurbitacins , a group of active ingredients of certain pumpkin plants, which stops in combination with carbaryl corn rootworm to eat. This is intended to keep the pest in the infested field and prevent infestation of neighboring regions. The product is sold under the Slam brand. In Hungary, Invite EC and Cidetrak are being tested, but they are dangerous to bees.

Transgenic corn

→ Main article: Transgenic corn

The use of Bt maize is a widely used alternative for combating the corn rootworm and European corn borer . However, since 2011 resistance to the Bacillus thuringiensis toxin has been described in corn rootworms from the USA.

Biologically

In the USA, certain ground beetles, rove beetles, predatory flies, parasitic wasps ( Braconidae ), spiders and roundworms ( nematodes ) have been identified as natural opponents . In addition, the pests also contract entomopathogenic fungi such as ( Beauveria and Metarhician ). Entomopathogenic nematodes have been tested with good success in Hungary, Austria and Italy. A first product based on the nematode Heterorhabditis bacteriophora called dianem has been on the market since 2012. When sowing, the nematodes are applied directly into the open seed furrow and parasitize the larvae of the corn rootworm. The roundworms penetrate the larvae and secrete a symbiotic bacterium there. The corn rootworms die from this infection after 1–2 days. The nematodes multiply in the larvae, leave the dead insects and parasitize further Diabrotica larvae. The continuous increase creates a lasting effect, there is no development of resistance. Heterorhabditis bacteriophora are beneficial organisms that are harmless to humans and animals. The use of plant extracts such as pyrethrins or Rotenone have also shown success against the corn rootworm. This control proved to be too expensive and therefore uneconomical. According to the Austrian Agency for Health and Food Safety, European studies are currently underway into the use of a parasitic fly (family Tachinidae ), which is a natural enemy of the corn rootworm in Mexico.

In Austria, a product has been developed to protect against the May rootworm which makes the mating disruption method applicable to agriculture: the female beetles give off scents, so-called pheromones , to attract the males. If a higher concentration of artificially produced pheromones is applied to a maize field, the males become disoriented, can no longer find their way to the females and generally become sexually inactive. This prevents the pest from multiplying. The application takes place on a special mineral as a carrier material, whereby a "slow-release" effect is achieved almost over the entire flight time of the corn rootworm. In addition, this enables application by spraying with a high level of economy. This product has been in use since 2015.

Monitoring

The beetle can be exterminated if there is a selective infestation. That is why the EU relies on the monitoring procedure, i.e. the targeted monitoring of potential risk areas (maize fields and transshipment points such as airports and shipping ports, barracks, motorway service stations). For using this insect trap which pheromones include and attract so male beetles. In Europe, attractant traps are usually used, which were developed at the University of Budapest by the Plant Protection Institute of the Hungarian Academy of Science. Monitoring has been in operation in Germany since 1997; In the last more than 1,100 traps, no infestation was detected until 2006; in 2007 it was discovered in the Ortenau district . Frankfurt Airport is indeed the hub of German aviation, but it does not present any potential danger because it is surrounded by kilometers of forests that do not provide food for the pest.

EU quarantine regulation

The western corn rootworm was notifiable until 2014. If the eradication failed, the affected state was obliged to counter any spread. Until then, the pest was considered a quarantine pest in the EU .

The decision of the commission of October 24, 2003 regulated the immediate measures against the spread of the harmful organism Diabrotica virgifera if it occurs occasionally ( i.e. not if it spreads naturally as e.g. in Austria):

In the infested zone

Insecticides were used for two years within a one kilometer radius of the infestation, and the harvest was limited so as not to scare away the pests and spread them further. The deadline was October 1st. The mandatory application of the three-year crop rotation was applied in the following years, which is only made as a recommendation after the regulation is repealed. Agricultural implements still had to be cleaned within the infested zone. Soil or plant stems were not allowed to be moved out of the affected area. This was especially true for the monocultures in the Rhine plain, Bavaria and northern Germany. A third of the German maize cultivation areas are monocultures. Organically operated farms are only allowed to use pyrethrin-containing insecticides after importation in order to retain their approval.

Maize cultivation bans in Baden-Württemberg

For 2008 and 2009 of were part of the Regional Council of Freiburg for the Ortenaukreis and by the Regional Council Tübingen in the field of Ueberlingen Lippertsreute ( Bodenseekreis ) maize cultivation bans imposed. 17 farmers from the Lahr area took legal action against the Freiburg administrative court and 9 farmers from the Lake Constance district at the Sigmaringen administrative court. Both courts confirmed the measures taken by the regional councils as lawful.

In the security zone

The security zone was another five kilometers around the infested zone. Here a crop rotation of at least two years had to be observed or alternatively insecticides had to be used for two years. The installation of pheromone traps was mandatory here.

Quarantine regulations and measures in Switzerland

In Switzerland, the corn rootworm is still classified as a quarantine pathogen as of 2019 . Since 2003, specimens of this species have been found in pheromone traps in several cantons of Switzerland. In order to prevent the spread, extensive measures are regulated: “According to Annex 1, Part A of the Ordinance on Plant Protection of October 27, 2010, PSV; SR916.20, MET is considered a particularly dangerous harmful organism, the reporting and control of which is mandatory in Switzerland. "

research

The urgency of the problem has now been recognized and solutions are being sought intensively.

Worth mentioning are the EU's DIABR-ACT project , which is coordinated by the University of Göttingen in Germany and the ARVALIS Institute in France, as well as the FAO Trust Fund for Food Security and Food Safety, which operates in Eastern Europe (Bulgaria, Bosnia-Herzegovina, Croatia, Romania , Serbia and Montenegro, Slovakia and Hungary).

Further classifications

See also

Press

  • Bernd Dörries: The One Billion Dollar Beetle . In: Süddeutsche Zeitung , No. 213, 15./16. September 2007, p. 12.

Web links

Commons : Western corn rootworm  album with pictures, videos and audio files

Individual evidence

  1. ↑ Ages: Corn rootworm , last changed: March 10, 2016
  2. ↑ Miller, Nicholas, Arnaud Estop, Stefan Toepfer et al. (2005): Multiple Transatlantic Introductions of the Western Corn Rootworm , in: Science, Vol. 310, p. 992, doi : 10.1126 / science.1115871
  3. ↑ n-tv.de: For the first time in Germany - corn rootworm discovered , July 24, 2007
  4. ^ Ministry of the Environment RLP: Corn rootworm forces cultivation ban and crop rotation - Minister Höfken initiates round table on August 28, 2012
  5. ↑ raiffeisen.com - Corn rootworm turns Lombardy into a disaster area
  6. ↑ biosicherheit.de - Corn rootworm causes massive crop failures in northern Italy
  7. ↑ Gerlinde Nachtigall: According to studies by the Julius Kühn Institute, seeds dressed with clothianidin are the cause of current damage to bees in Baden-Württemberg. Julius Kühn-Institut (JKI), May 16, 2008, accessed on May 21, 2020 (press release by the Science Information Service ).
  8. ↑ http://www.diabrotica.de/Informationen
  9. ↑ Aaron J. Gassmann, Jennifer L. Petzold-Maxwell, Ryan S. Keweshan, Mike W. Dunbar, Peter Meyer: Field-Evolved Resistance to Bt Maize by Western Corn Rootworm. In: PLoS ONE. 6, 2011, p. E22629, doi : 10.1371 / journal.pone.0022629 .
  10. ↑ dianem® . Product for biological pest control of the corn rootworm by nematodes.
  11. ↑ Confuse the corn rootworm . In: landwirt.com . ( landwirt.com [accessed April 18, 2018]).
  12. ↑ Lukas Weninger: With pheromones against the corn rootworm . In: top agrar Austria . ( topagrar.at [accessed on April 18, 2018]).
  13. ^ Ordinance repealing the ordinance to control the western corn rootworm
  14. ↑ Agroscope (Federal Department of Economics, Education and Research): Corn rootworm (Diabrotica virgifera virgifera) ( Memento of July 24, 2019 in the Internet Archive ) As of July 2019.
  15. ↑ Federal Office for Agriculture FOAG, Agroscope (Federal Department of Economics, Education and Research), Guideline No. 6: Control of the corn rootworm (Diabrotica virgifera virgifera) ( Memento of July 24, 2019 in the Internet Archive ), July 16, 2019 edition.