New study shows that flying predators are top crop savers –
but to reap the benefits farmers need to plant flower-rich margins

A three year study by the Game & Wildlife Conservation Trust that has involved infesting acres of farmland with nearly 200,000 cereal aphids (Sitobion avenae) has revealed that growing flower-rich margins on farmland could lead to more effective natural control of these troublesome farmland pests by boosting their natural enemies such as rove beetles, hoverflies and other predatory flies.  This process is known as bio-control. 

The Trust has been leading research on the use of pesticides on farmland since the 1960’s when its researchers were the first to establish the link between the intensification of agriculture, particularly the harmful effects of insecticides and the sudden decline of farmland birds and gamebirds such as the wild grey partridge. This latest study should provide further evidence to farmers that bio-control is a viable option in the battle to control cereal aphids while helping to conserve farmland birds and other wildlife.

In controlled field trials, the GWCT scientists released thousands of cereal aphids into specially designed enclosures located on arable farmland in the south of England.  The rate at which ground and flying predators controlled the aphid infestations was compared against the creation of standard field margins (2 m wide) and wider field margins (6m wide).  The research showed that flower-rich habitats were particularly good at attracting and supporting a wide range of natural flying enemies, while tussocks of grasses established along beetle banks supported high densities of overwintering ground dwelling insects such as beetles and spiders.

The experiment clearly showed that when all predators were present, the flying predatory insects were the most effective at bio-control and managed to reduce aphids by 90%.  Ground predators such as beetles and spiders were also beneficial but worked more slowly than their aerial counterparts, probably because the flying predators are more mobile, quickly locating the aphid colonies.
 
To provide the right level of bio-control  to reduce aphid infestations, the study suggests that despite the importance of aerial predators, ground predators are also a valuable factor and therefore to achieve a robust bio-control system it is necessary to encourage a diverse range of natural enemies through habitat management  This would ensure that natural fluctuations in the populations of different beneficial predators that occur within and between fields are compensated for by encouraging different groups.

Dr John Holland, head of farmland ecology with the Trust said, “The study, which was published in the science journal Biological Control showed that to maximise the benefit of these valuable predators it is essential to establish a rich variety of seasonal habitats that provide over-wintering sites as well as flower-rich habitats, which contain plants such as knapweed, cow parsley, yarrow and wild parsnip in summer.  These not only boost beneficial flying predators but they also provide good habitats for other important insects such as bees and other pollinating insects such as butterflies.”

Although flower-rich margins are the best habitat for a range of insects, it appears that under current agri-environment schemes that pay farmers to manage the land for wildlife, very few farmers are electing to grow these important habitats, preferring instead to concentrate on the easier option of growing grass margins.  Dr Holland, explains, “Grass margins are of limited benefit to wildlife, but if you add flowers these not only boost numbers of flying predatory insects they also help declining bees and other important pollinating insects. 

Dr Holland continues, “However, establishing flower-rich margins is not an easy option and can be more expensive to establish.  We believe that our research shows the importance of this habitat to a wide range of species and this should be reflected in the development of future Stewardship payments to farmers.”   

You can read more about this this study by the Game & Wildlife Conservation Trust at http://www.gwct.org.uk/research__surveys/biodiversity__ecosystems/farmland_biodiversity/integrated_pest_management/1097.asp or  please Contact  Dr John Holland, head of farmland ecology the Game & Wildlife Conservation Trust, Telephone: 01425 651035, mobile: 07711 680585 or Morag Walker, Head of Media, Telephone : 01425 651000 or mobile: 07736 124097.

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Aphid facts:

1. Aphids are a major pest of cultivated plants.  4000 species are known of which 250 are serious pests causing damage by sucking plant sap and transmitting plant viruses.

2. Some are born already containing live embryos.  Females can reproduce without mating.

3. One female cabbage aphid can, in a year, theoretically produce over 12 generations of young or 257,000 million offspring, weighing 822 million tons.

4. Thankfully, this reproductive capacity is never reached.  Aphids are eaten by a range of specific predators, (ladybirds, hoverfly larvae) and generalist predators (spiders, ground beetles).

5. Some aphids produce a sweet substance called honeydew.  Colonies of ants protect the aphids from predators in return for this sugary bounty.

Photocaption:  A new study by the Game & Wildlife Conservation Trust has revealed that growing flower-rich margins boosts the number of natural aphid enemies such as this hoverfly and thus reduces the need for pesticides. Hoverfly larvae will consume nearly 400 aphids before they pupate.

Notes to editors

The Game & Wildlife Conservation Trust is an independent wildlife conservation charity which carries out scientific research into Britain’s game and wildlife. We advise farmers and landowners on improving wildlife habitats and we lobby for agricultural and conservation policies based on science. We employ 14 post-doctoral scientists and 50 other research staff with expertise in areas such as birds, insects, mammals, farming and statistics.  We undertake our own research as well as projects funded by contract and grant-aid from Government and private bodies.   The Trust is also responsible for a number of Government Biodiversity Action Plan species and is lead partner for grey partridge and joint lead partner for brown hare and black grouse.

For Information, contact
Morag Walker, Head of Media
Telephone: 01425-652381
Direct:  01425-651000
Mobile: 07736-124097