Trying to Find Pest Solutions While Hoping Evolution Doesn’t Exist Doesn’t Work

Posted on May 5, 2010  Comments (2)

How To Make A Superweed

Melander wondered why some populations of scales were becoming able to resist pesticides. Could the sulfur-lime spray trigger a change in their biology, the way manual labor triggers the growth of callouses on our hands? Melander doubted it. After all, ten generations of scales lived and died between sprayings. The resistance must be hereditary, he reasoned. He sometimes would find families of scales still alive amidst a crowd of dead insects.

This was a radical idea at the time. Biologists had only recently rediscovered Mendel”™s laws of heredity. They talked about genes being passed down from one generation to the next, yet they didn”™t know what genes were made of yet. But they did recognize that genes could spontaneously change”“mutate”“and in so doing alter traits permanently.

In the short term, Melander suggested that farmers switch to fuel oil to fight scales, but he warned that they would eventually become resistant to fuel oil as well. In fact, the best way to keep the scales from becoming entirely resistant to pesticides was, paradoxically, to do a bad job of applying those herbicides. By allowing some susceptible scales to survive, farmers would keep their susceptible genes in the scale population. “Thus we may make the strange assertion that the more faulty the spraying this year the easier it will be to control the scale the next year,” Melander predicted.

What”™s striking is how many different ways weeds have found to overcome the chemical. Scientists had thought that Roundup was invincible in part because the enzyme it attacks is pretty much the same in all plants. That uniformity suggests that plants can”™t tolerate mutations to it; mutations must change its shape so that it doesn”™t work and the plant dies. But it turns out that many populations of ryegrass and goosegrass have independently stumbled across one mutation that can change a single amino acid in the enzyme. The plant can still survive with this altered enzyme. And Roundup has a hard time attacking it thanks to its different shape.

Another way weeds fight off Roundup is through sheer numbers. Earlier this year an international team of scientists reported their discovery of how Palmer amaranth resists glyphosate. The plants make the ordinary, vulnerable form of the enzyme. But the scientists discovered that they have many extra copies of the gene for the enzyme”“up to 160 extra copies, in fact.

What makes the evolution of Roundup resistance all the more dangerous is how it doesn”™t respect species barriers. Scientists have found evidence that once one species evolves resistance, it can pass on those resistance genes to other species. They just interbreed, producing hybrids that can then breed with the vulnerable parent species.

Another great article from Carl Zimmer.

Related: Amazing Designs of LifeMicrocosm by Carl ZimmerParasite RexPigs Instead of Pesticides

2 Responses to “Trying to Find Pest Solutions While Hoping Evolution Doesn’t Exist Doesn’t Work”

  1. Drug Resistance Isn’t Just for Infections Anymore « Pasco Phronesis
    May 9th, 2010 @ 9:52 pm

    […] after overuse – the same is true of weeds, pests, and herbicides.  Carl Zimmer writes (H/T Curious Cat) about how agricultural pests have developed resistance in the early part of the 20th century.  […]

  2. Evolution in New York City Wildlife » Curious Cat Science Blog
    August 1st, 2011 @ 1:19 am

    Lots of life manages to survive the challenges of urban life and it is interesting to learn what scientists are finding about that life…

Leave a Reply