In potato crops, this led to fewer insect pests and larger potato plants.

“It’s always been a mystery how organic farmers get high yields without using synthetic insecticides,” says co-author Bill Snyder, associate professor of entomology at Washington State University. “Our study suggests that biodiversity conservation may be a key to their success.”

Ecosystems with more total species, and more beneficial species that are relatively evenly distributed, are thought to be healthiest. The use of insecticides can harm biodiversity by reducing the number of species and by making some species (often pests) much more common than others. The study, which was funded by USDA’s National Institute of Food and Agriculture (NIFA) and published in the July 1 edition of the journal Nature, shows that organic farming practices lead to many equally common beneficial species, and that this reduces pest problems.

In potato fields that used conventional control practices (e.g., applications of broad-acting insecticides), usually just one species of beneficial predatory insect or pest-killing pathogen was common. In contrast, in organic fields several beneficial species were about equally common. Experiments showed that groups of evenly abundant beneficial species, typical of organic farms, were far more effective at killing potato beetle pests. Because natural enemies are usually more even in organic crops of many different kinds, not just potato, these benefits could be widespread.

NIFA funded this project through the National Research Initiative Arthropod and Nematode Biology and Management competitive grants program.