A NEW £1m field study will start next spring to find out how much land must be devoted to beetle banks and similar areas favouring indigenous biocontrol insects in order to cut the use of insecticides.

The ‘Rebugging the system‘ project, backed by a new DEFRA/Research Council Rural Economy and Land Use initiative, will be undertaken by the Game Conservancy Trust, Rothamsted Research and Imperial College.

“We are trying to measure the amount of insect-rich habitat that is needed to produce an effect,” explained GCT entomologist John Holland.

“No-one has investigated it on this scale before. Our aim is to see how much land needs to be manipulated to create good habitat before you encourage beneficial insects sufficiently to achieve natural pest control.”

The work, based on prescriptions in the government‘s Agri-environment schemes, will focus on adding six metre flower-rich mixed-grass strips at field margins.

These are known to attract both predators and parasitoids of pests like aphids, noted Dr Holland.

Insect response will be monitored both on a field scale and on a wider basis, possibly whole estates, and the GCT is seeking help from a range of farms in southern England.

The idea, using a specially designed exclusion technique, is to assess the impact on aphids of parasitic wasps, hoverflies and predatory beetles in four replica areas and four controls with standard field margins.

Each area will be infested with a fixed number of aphids in late May.

The monitoring will identify the contribution each makes to control and see how this is influenced the scale of habitat manipulation, he explained.

“We have over 500 different species of insects and spiders living in cereal fields. Only 10 of these species are a problem to our crops, but their effect can be devastating.”