Iconic insects are disappearing

The monarchs are late. Usually by the 1st of November, the forests of central Mexico are swarming with them. Last year, they came in record low numbers, only 60 million. This year? A week late and only 3 million. And this happening to insects across the spectrum.

A big part of it is the way the United States farms. As the price of corn has soared in recent years, driven by federal subsidies for biofuels, farmers have expanded their fields. That has meant plowing every scrap of earth that can grow a corn plant, including millions of acres of land once reserved in a federal program for conservation purposes.

Another major cause is farming with Roundup, a herbicide that kills virtually all plants except crops that are genetically modified to survive it.

As a result, millions of acres of native plants, especially milkweed, an important source of nectar for many species, and vital for monarch butterfly larvae, have been wiped out. One study showed that Iowa has lost almost 60 percent of its milkweed, and another found 90 percent was gone. “The agricultural landscape has been sterilized,” said Dr. Brower.

• biology