Organic Agriculture Improves Natural Pest Control
Organic farming practices support biodiversity, and diversity - in the form of both species richness and relative abundance - improves natural pest control.
These are the findings of a paper published in Nature ("Organic agriculture promotes evenness and natural pest control" sub. req.) by Washington State University post-doctorate research associate David Crowder and colleagues.
From the Nature news article, "How to get even with pests," by Lindsay A. Turnbull and Andy Hector:
There is little doubt that organic farms generally support more biodiversity, with a higher abundance and greater species richness of many plant and animal groups (Bengtsson et al. 2005). ... However, ecologists have been challenged to provide evidence that the increased biodiversity on organic farms actually leads to a better ecosystem service in the shape of better pest control (Letourneau & Bothwell 2008).
Diversity itself has two components: species richness (the number of species) and species evenness (the relative abundance of those species). Species richness and evenness can vary independently, so communities can contain the same number of species but still differ in evenness.
And from the Crowder et al. paper:
In our potato system, the evenness increase between conventional and organic farms translates into pest densities 18% lower and plants 35% larger, suggesting that benefits of evenness for pest control may somewhat offset yield losses to reduced insecticide use. ...
Our results strengthen the argument that rejuvenation of ecosystem function requires restoration of species evenness, rather than just richness. Organic farming potentially offers a means of returning functional evenness to ecosystems.