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Natural pest control

03 February 2009

A cabbage white butterfly, one of the pest species reared on the farms studied for the researchA cabbage white butterfly, one of the pest species reared on the farms studied for the research

A study of natural pest control on conventional and organic farms in the southwest of England has found no difference between the two systems.

The team, which involved Dr William Symondson, of the School of Biosciences, has shown that caterpillars are attacked by parasitic wasps to the same degree on both conventional and organic farms.

The research, which is published in the journal Ecology Letters in March, adds to a body of work that aims to find out which farming methods and practices yield the optimum crop production, with minimum impact on the environment.

Previously, it has been asserted that increased biodiversity on organic farms would equate to better natural pest control than on conventional farms, but this research suggests that in fact, natural pest control can be as effective on either type of farm.

The work confirms that there are more species of both plants and insects on organic farms than on conventional farms - a result that may seem obvious - however, previous studies have given contradictory results because they have been small in scale and narrowly focused.

This large scale study included the whole farm system, taking into account fields where crops are grown as well as non-crop areas such as hedgerows and woodland. The results suggest that in fact natural pest control is no better or worse in either farm system, at least in the South West of England where this study was conducted.

To find out how effective natural pest control is on each farm, the researchers also introduced a non-native species of leaf miner - an insect that eats leaves from the inside out - that feeds on the shrub Pyracantha. A small patch of Pyracantha plants was also introduced, and the team monitored how well the leaf miners did in the face of natural pest control by parasitic wasps, which occur naturally in the farm environment. The leaf miners were controlled equally as well on both types of farm.

Scientists have traditionally looked to so-called indicator species such as bumble bees and farmland birds as a measure of biodiversity. However, rather than focusing in on just one group, the team used a method that gives a holistic picture of the ways in which a whole community of species interact.

Dr William Symondson said "It is sometimes forgotten that the increase in species diversity and abundance on organic farms may mean that there are not only more predators but also more prey for them to attack. Thus, the ratio of predators to prey - including pest species - may be the same, which may explain our finding."

The research was funded by the Biotechnology and Biological Sciences Research Council and was led by Professor Jane Memmott of the University of Bristol.

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