PARIS — Supporters of organic agriculture got a boost on Thursday with a scientific study that said pesticide-free potato farming improved control over crop-munching insects and delivered bigger plants.
David Crowder, an entomologist at Washington State University, led a team that reviewed published data about local potato fields, looking in particular at plant-chewing beetles and the bugs and fungi that prey on them.
The big focus was not so much on the tally of the various species — the traditional benchmark of biodiversity — but the “evenness” of them.
In other words, whether the species were roughly balanced in numbers or whether one particular species dominated.
In organic fields, where the use of agricultural chemicals was closely controlled, pests and predators evened out, the researchers found.
Pest densities in these fields were 18 percent lower, and potato plants were 35 percent larger, than in conventionally-farmed fields.
The scientists put the findings to the test in an experimental field in which they deliberately manipulated insect numbers.
The researchers suggest that pesticides disrupt the balance between natural enemies.
As a result, fields become dominated by just a few species, which enabled pests — unchallenged by sufficient predators — to swiftly become a major problem.
In conventional fields, just one species accounted for up to 80 percent of insects that were counted.
But in organic fields, the most dominant species comprised as a little as 38 percent.
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