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DIABROTICA
Threat to European maize production by invasive quarantine pest, Western corn rootworm (Diabrotica virgifera virgifera)

Key processes enabling the recently introduced maize pest, the western corn rootworm (WCR), to invade central parts of Europe and possibilities for controlling this species will be examined by seven partners. Each of the partners offers expertise in crop management, plant-insect interactions, natural enemy evaluation, risk management and biotechnological control methods. The development of a practical approach for the management of this new insect pest species is urgent, due to continual invasion. Its potential establishment in Italy confirms theories that WCR will threaten maize production areas in other EU member countries in Central Europe in the immediate future. By combining work on the ecology of WCR with work on applied aspects of maize production, we will be able to develop and establish a safe and environment-friendly crop management practice, adapted to specific maize production systems in Europe.


Objectives
The overall objective of the research is to develop and incorporate sustainable, biologically-based crop management practices for European maize production to maintain high-yield maize production requiring less use of chemical pesticides. The specific objectives for a sustainable control of WCR are as follows:
1) to characterise plant stimuli which trigger the host plant preferences and the egg laying behaviour of WCR
2) to test European corn varieties (non-GMO and GMO) and related non-cultivated plant species for their potential as food resources
3) to identify natural enemies in Europe and in the area of origin in Central America
4) to improve existing methods for the monitoring of WCR
5) to improve mating disruption techniques to assist in the control of WCR
6) to model the potential economic consequences of different scenarios of invasion of the WCR into European Union countries
7) to analyse the cost/benefits of containment strategies to prevent further spread of WCR.

Progress to Date
In the second reporting period, Diabrotica carried out research on ecological, distributional and behavioural aspects of WCR and continued with research on the impact of crop rotation on the abundance of WCR in Hungary, and eradication measures in Italy.
Research on the feeding behaviour of WCR adults in fields in southern Hungary have continued and the preference of WCR for particular plant and weed species has been established. Adult feeding is much more variable than was regarded in the past, depending on the resources available. These findings relate to crop rotation experiments where a slight adaptation of WCR egg laying to the crop rotation system can be seen. These findings may have profound implications on the recommendation for integrated crop-managing strategies.
The chemical analyses of the plant surface compounds, which influence the alighting and ovipositing behaviour of WCR females, revealed differences regarding the maize cultivars tested to date. The potential for plant breeding resulted in antixenotic behaviour in the females. The high diversity and variable content of both sugars and amino acids on the plant surfaces offer a realistic opportunity to enhance the resistance of new cultivars to cope with this new pest within Europe.
The identification of European areas with a high density of maize production, in combination with climate data, made it possible to simulate the spreading of the WCR population with and without containment measures, again demonstrating the ability of WCR to quickly invade areas not yet infested. The high-risk areas identified so far should be regarded as focus areas where the results of the Diabrotica project should be implemented after WCR invasion.
The crop rotation experiments in southern Hungary demonstrate the difficulties in finding simple solutions for the management of WCR, because the ability of WCR females to adapt to diversified crop-rotation systems seems to be higher than expected, with reference to the North American results. Data from the third year of this work package will be important for making recommendations for the management of WCR.
The measures taken around Venice to eradicate the isolated WCR populations detected several years before were successful. However, the detection of an additional population in northern Italy demonstrates the high invasive potential of WCR, which is currently not fully understood in detail. The development of a new trap-type, and recommendations for the use of different trap-types already available, will serve as a keystone in the establishment of monitoring routines to assess the spreading of WCR in Europe in the future.
The mating disruption technique, which will be established within the Diabrotica project, demonstrates both the problems and potential in the use of this unique method. Progress achieved by the responsible partner is encouraging to date; methodological problems addressed in the first progress report have been solved and the use of MCA as an orientation disruptant has been demonstrated in the field. The third period of field experiments could therefore concentrate on improving the mating disruption and could help in discussing the implementation of this method in regularly applied managing options.
Life table studies on WCR populations, carried out in southern Hungary during the second year, indicate that natural enemies of WCR are limited at the moment, and that the impact of naturally-occurring pathogens and nematodes is one important source of mortality, acting on larval populations. However, high winter mortality rates could be due to harsh climatic conditions in this region, resulting in a negative intrinsic rate of increase.

Results
Research on the feeding preference of WCR in fields in southern Hungary confirmed a large array of host plants (including weeds), which could serve as alternative food resources for WCR adults. However, larval feeding on the plant roots is restricted mostly to maize cultivars. Differences in the suitability of certain cultivars demonstrate the potential of breeding for resistance of maize for WCR. No differences were found when comparing the suitability of Bt-corn varieties and their isolines, engineered for control of the European corn borer. Detailed studies on the egg-laying behaviour and on the morphology of sensilla of WCR form the baseline for analyses of those metabolites on the plant surface, which trigger female alighting and egg laying. The first results are promising regarding the differences in the acceptance of certain maize cultivars, separated by their sugar and amino acid content profiles. The spread of WCR into Germany, serving as a first example, has been successfully simulated for different scenarios, demonstrating that eradication measures would help to decrease the process of spreading WCR. Moreover, the conditions for the development of WCR populations regarding temperature regimes have been simulated. The data on the maize production areas in several EU countries have been compiled, helping to identify high-risk areas in EU countries. The ongoing programme to eradicate isolated WCR populations in Italy clearly demonstrates that the strategies implemented in a focus area around Venice proved very effective in reducing WCR populations; the key factor of eradication/containment of this species being the interruption of maize monoculture. However, due to the detection of new infested areas in Lombardy and Piedmont, the programme was extended to include these new populations.

Research on the development of a suitable trap-type to monitor WCR led to a new trap-type being developed, which is less expensive and more suitable in most monitoring situations compared to other trap-types recommended in the past. The methodological problems involved in establishing the mating disruption techniques have been further evaluated and, generally, solved; the distribution patterns of MCA-coated grids have been successfully evaluated in the field. Orientation disruption in the field was recorded after aerial application of the coated grids, demonstrating the potential of this method to serve as an additional measure for the control of WCR populations. Research in the remaining year will help in establishing routines of application protocols and the understanding of which factors trigger the mating disruption of WCR. The crop rotation experiments were successfully established for a second year in Hungary. The results analysed to date indicate the possibility of a slight adaptation of WCR adults to the European crop rotation system, showing a preference for corn, but occurrence in other crop stands was observed. However, these important findings have to be validated in the third year of the crop rotation experiment. A life table for WCR populations in southern Hungary has been developed, indicating the over-wintering and first instar larval mortality being the k factors in the population dynamics of WCR. The number of natural enemies of WCR to date is very poor in Europe, so the selection of an exotic natural enemy seems the only way of naturally controlling WCR in the field. Although a tachinid fly (Celatoria compressa) seems promising with regard to host specificity to Diabroticinae beetles, more research is needed to decide whether the option of introducing this parasitoid species to Europe should be taken or not.

Classified in CEREALS, ARABLE CROPS, CROP PESTS AND DISEASES, GENOMICS

Scientist responsible for the project

Prof STEFAN VIDAL
Grisebachstrasse 6
37077 Goettingen
Germany - DE

Phone: +49 551 399744
Fax: +49 551 394187
E-mail: svidal@gwdg.de

References

Project ID QLRT-1999-01110
Organisation Institut for Plant Pathology and Plant Protection-Section Agricultural Entomology
Area 5.1.1
Start date 01 February 2000
Duration (months) 36
Total cost 1 594 011 €
Total EC contribution   1 116 037 €
Status Completed

The partners

  • Institut National de la Recherche Agronomique-Unité de Phytopharmacie et Médiateurs Chimiques, France - FR
    derridj@versailles.inra.fr
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