David Crowder, WSU, with trials of potato plants.   Courtesy of Shelley Hanks, WSU.

An article published in Nature magazine claims that the more "balanced" ecosystems (animal and plant communities) typically seen in organic agriculture work to better protect the plant from attack by pests and result in improved plant growth.

Analysing the insect pests and their natural enemies in potato crops showed that with organically grown plants, there was no one insect species dominant.  It was also found that the crops grown with more balanced insect populations grew better.

The researchers from Washington State University and the University of Georgia were led by David Crowder, a post-doctoral research associate in entomology at WSU.  They looked at potato crops in Washington and found that on conventional farms, a single insect species may account for 80% of the total insect population.  On organic farms, on the other hand, the highest level found for a single species was 38%.  They tested field observations on trial plots at WSU.

Using field enclosures on WSU's Pullman campus, Crowder recreated those conditions using potato plants, Colorado potato beetles, four insect species and three soil pathogens that attack the beetles. When the predators and pathogens had similar numbers, says Crowder, "we would get significantly less potato beetles at the end of the experiment."  "In turn," he adds, "we'd get bigger plants."

The results suggest that not only the richness, but also the evenness, of the insect population needs to be considered in restoring an ecosystem.   Major potato users (French fry sellers) are being pressured by consumers to give greater consideration to the ecological sustainability of different pest-control practices.  The results obtained by these researchers may lead to changed practices in future.

The WSU media release is at: http://www.wsutoday.wsu.edu/pages/publications.asp?Action=Detail&PublicationID=20565

Science Daily report at: http://www.sciencedaily.com/releases/2010/06/100630132752.htm