Defra

The Western corn rootworm, Diabrotica virgifera virgifera, was first confirmed on five farms in the vicinity of London Heathrow and Gatwick airports in 2003. In 2004, the beetle was found in the same two areas in similar numbers to 2003, but was not detected in any new locations following an extensive national survey.

The 2005 survey comprised

1) A national survey to monitor maize-growing areas throughout the UK

2) Increased monitoring of maize fields in an extended buffer zone within 20km of outbreak farms

3) Continued intensive monitoring in the Safety Zone (<6km of outbreak farms) and in the Focus Zone (1km).

Results

- No beetles were found in those fields where beetles had been trapped in 2004, confirming the effectiveness of crop rotation as the recommended control measure against this pest.

- No beetles were confirmed in 2005 on the existing outbreak farm in the Gatwick area

- A significant increase in beetle numbers was recorded in the Heathrow area despite the use of insecticide-treated maize seed.

- Particularly high numbers of beetles were confirmed on a new outbreak farm within the 6km Safety Zone, near Heathrow airport.

- Increased monitoring in 20km buffer zones around the 2004 outbreak farms have also resulted in findings of low levels of beetles at 5 new farms.

Recommended Control Measures

Crop rotation is the most effective means of control. Maize growers, particularly in the south of England, are advised to rotate maize with alternative crops wherever possible. This helps to break the life cycle of the pest. Larval stages hatching in spring from eggs laid in the soil will starve if no maize roots are available to feed on.

Avoid maize or rotate game cover crops as this provides a reservoir of the pest and poses a risk to maize crops in the surrounding area. Use non-maize seed mixes wherever possible or rotate maize grown for game cover.

The effectiveness of seed treatments under UK conditions remains unknown. However, large numbers of beetles have emerged in maize fields in the Heathrow outbreak area, where imported seed had been pre-treated with imidacloprid (e.g.“Gaucho”).

Further details on the western corn rootworm, including recognition, life-cycle, pest status and action being taken in the UK, can be found in the Plant Pest Notice (pdf) updated on Western corn rootworm. A Pest Risk Analysis (PRA) (pdf) is also available.

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