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WCR (Western Corn Rootworm) - Recommendations for the use of conservation and cultural practises to enhance the effectiveness of native European mortality factors

Provision of supplementary food (e.g. food spray, pollen, nectar): Presence of wild flowers can increase food sources for parasitoids in crops. Minor negative impact is expected due to additional pollen supply for adult WCR (Western Corn Rootworm) when maize starts drying.

Provision of refugia for overwintering: Overwintering refugia such as grass strips or remaining crop plant material after harvesting can increase survival of natural enemies in maize and can increase survival of WCR eggs.

Maintenance of non-economic levels of hosts or alternative prey / hosts over time to ensure survival of natural enemies: As there are no specific natural enemies known on D. v. virgifera in Europe the maintenance of a low population of this pest is not necessary as long as alternative hosts, e.g. other insect larvae or adult, are available for generalist predators. Those will be available when non - crop plants and their herbivores remain in or around fields.

Composition of non - crop vegetation within and around fields, Pro and contra of weeds: Weeds are a major problem in maize production. On the other hand non - crop plants within and around fields can benefit natural enemies e.g. the presence of wild flowers increases parasitoid abundances. Some entomophagous insects are attracted or arrested by chemicals released by the herbivore hosts plant or by associated plants, which can be investigated as soon as specific natural enemies against D. v. virgifera are known.

Outbreaks of crop pests are more likely to occur in weed free fields than in weed diversified crop systems, which were also shown for maize. Thus presence of tolerable levels of weeds should be achieved. Minor negative impact of weeds are expected due to additional pollen supply for adult WCR when maize starts drying (especially Ambrosia spp, and Sunflower), due to higher oviposition rates of Diabrotica beetles at higher plant coverage and due to competitions between weeds and young maize plants.

Use of kairomones: No kairomone is known to attract specific natural enemies in the European maize system

Increasing environmental heterogeneity and complexity of agricultural areas: Vegetation mosaics and corridors in the agricultural areas are important for enhancing natural enemies, e.g. parasitism levels of Ostrinia nubilalis in maize near wooded sites were found to be higher. Additionally high crop diversity through mixtures in time and space generally enhance natural enemies.

Soil type: Soil type is difficult to change, although it has an influence on ground living predators and on the survival of D. v. virgifera larvae.

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