Re-bugging the system

There is widespread concern about the use of insecticides in food production and there is considerable research into potentially viable biological control alternatives, but pest control in UK field crops relies mostly on chemical pesticides.

Pest thresholds help to ensure insecticides are only applied when economic damage threatens, but the lack of adoption of bio-control is mainly because we know little about the natural predators that act as control agents.

With our partners from  Rothamsted Research and Imperial College, London, we are evaluating the relationships between pests and their predators and parasitoids (parastic wasps), and how these are affected by natural habitats such as hedgerows and field margins. Further information on the project is available from the Rebug website.

We have found that predators that fly (eg. hoverflies, parasitic wasps and long-legged flies) are more effective at reducing the number of cereal aphids than ground-active ones (eg. beetles and spiders). We also found that the presence of six-metre-wide flower-rich field margins made little difference to the abundance of these predators in an area where there was plenty of natural habitat (see Figure 1).

However, we did find that fields surrounded by six-metre grass margins contained a significantly greater number of money spiders, soldier beetles and aphid-eating rove beetles than fields without a margin (see Figure 2),  and the total number of aphid predators flying over the field was significantly greater earlier in the season (beginning of May) where a margin was present.  However, these predators may disperse further than a single field early in the season.

By positioning traps at different distances from the field margin (20m, 40m and 80m) we were able to determine how far from the field margin they could fly.

Long-legged flies were unable to fly very far from the field margin, whereas lacewings and soldier beetles showed the opposite trend, as they may have been searching for aphid prey or, in the case of lacewings, aphid patches within which to lay their eggs (see Figure 3).