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Importance of arthropod pests and their natural enemies in relation to recent farming practice changes in the UK

RESEARCH REVIEW 64

Importance of arthropod pests and their natural enemies in relation to recent farming practice changes in the UK

by
J M Holland1 and J Oakley2

1 The Game Conservancy Trust, Burgate Manor, Fordingbridge, Hampshire SP6 1EF
2 ADAS UK Ltd., Woodthorne, Wergs Road, Wolverhampton, WV6 8TQ

June 2007

Abstract

Pressure to reduce insecticide use and increase farmland diversity is encouraging farmers to employ a range of approaches to reduce the impact of insect pests on crop yield and quality. Insecticide applications are often still required to prevent significant damage but these interact with other approaches and can undermine efforts to sustain functionally significant populations of beneficial insects. Populations of beneficial and pest insects are also influenced by a range of other factors including cultivations, climate, landscapes and rotations. Consequently, the population dynamics of beneficial and pest insects in arable agriculture are complex. In this review the economically important pests and beneficial arthropods in arable crops were assessed in the context of recent changes in farming practice.

Pests

The current and future status of the more important and potentially important pests of cereals and oilseed rape was reviewed. Information on incidence was drawn from specific surveys of incidence, where conducted, and reports from agronomists and farmers. The reasons for changing status were reviewed, with particular emphasis on any changes linked to climate change, changing farming practice and landscape issues. Milder winters have increased the importance of those pests active during the winter, especially aphid virus vectors transmitting BYDV and oilseed rape viruses. Warmer spring and summer temperatures have resulted in outbreaks of other pests such as orange wheat blossom midge and turnip sawfly. Warmer autumn weather favoured pests such as gout fly and cabbage stem flea beetle. The provision of larger areas of grass margins favoured the traditional ley pests and pests such as the cereal ground beetle.

Natural enemies of cereal and oilseed pests

A list of all the natural enemies of cereal and oilseed rape pests was compiled from the literature. References on their biology and ecology were reviewed, along with opinions of relevant experts and a subjective scoring system devised to identify important gaps in knowledge. This revealed large discrepancies in the level of knowledge for different families and even orders of insects. Long-term trends in the abundance of natural enemies were reviewed using data from The Game Conservancy Trust Sussex study. Polyphagous predators showed consistent long-term declines, unlike the aphid-specific predators. These may be more vulnerable to intensive farming practices because many species are relatively immobile. Parasitica were probably responding to the trends in their hosts, but as they are not identified to species, this relationship could not be examined.
The options available under the Environmental Stewardship scheme, along with minimum tillage and Integrated Pest Management, were assessed to identify the types of natural enemies that they can support and for their potential to improve biocontrol. A subjective score was determined that indicated the potential of each habitat type for natural enemies. Overall well-managed hedgerows comprised a substantial shrubby component with a 2m wide floristically diverse hedgebase providing most resources. Relatively few of the options allow for manipulation of the cropped area even though this is important for some of the most abundant natural enemies (Carabidae, Linyphiidae and some parasitoids). Pest control using insecticide/molluscicide was considered by a panel of experts to remain the mainstay in the future, however alongside the use of natural enemies. To achieve such a balance would require further information and the use of reduced doses was seen as one possible way forward. Suggestions for future research are provided.

HGCA Project Number: 3302
Price: £6.50

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