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The Bedbug Boom and Unnatural Selection

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After disappearing from the U.S., bedbugs have made a dramatic comeback in the last decade.  Some conservatives have blamed environmentalists for the return of the bloodsucking pests – and in particular, Rachel Carson, author of “Silent Spring.”

A website called “Rachel Was Wrong,” for example, argues that the pesticide DDT was effective in eliminating bedbugs from the United States in the 1950's.  But then the Environmental Protection Agency banned DDT in 1972, inspired in part by Carson's book and the environmental movement she sparked.  Bedbugs came roaring back, the argument goes, because we had chemically disarmed ourselves.

Is this true?  I asked bedbug expert Dini Miller, Professor of Entomology Virginia Tech.

Miller said the first part of the claim is accurate: DDT did wipe out bedbugs in the U.S. But the story is more complex than that, she said, because countries in Africa, South America, and elsewhere around the world continued to use DDT and other insecticides against the pests. And the bedbugs, over time, developed resistance to these pesticides.  With globalization and increased travel between continents,  the bedbugs found it easy to hitchhike back into the U.S. as resistant superbugs.

“We have selected for the absolutely toughest bedbugs there are out there,” Miller said.  “And what seems to have happened is that they have become so resistant to insecticides that we have not been able to control their population growth. And when you have a lot more bedbugs, they spread out to find a lot more people to bite.”

How did this happen?  Through random mutations.  Most of the bedbugs were killed by DDT. But a few that had thicker skin -- or enzymes inside their bodies that can break down pesticides – survived. And  these survivors are the ones that reproduced, passing on their DNA to future generations.

It was an example of chemically-induced evolution.   Toxicologist and author Emily Monosson calls the phenomenon “Unnatural Selection” in her new book by the same title, which is subtitled, “How We Are Changing Life, Gene by Gene.”

 “We think that we can just use another chemical or more chemicals but really these efforts are  trumped by nature,” said Monosson, an adjunct professor at the University of Massachusetts, Amherst.  “Animals develop resistance.”

She points out that  it is not only bedbugs that are evolving rapidly to adapt to the human environment, but also bacteria like staphylococcus that are now resistant to antibiotics used excessively in hospitals and on farms.  Some plants like horseweed, pigweed, and waterhemp have evolved to resistance to the common agricultural herbicide Roundup. And even some fish, including tomcod and killifish, have evolved to tolerate high concentrations of toxic pollutants like PCB’s and dioxins.

Monosson writes: “We are laying the groundwork for a game of survivor Planet Earth.  And the outcome may not be to our liking.”

While a few species – like bedbugs, bacteria, and weeds – are able to adapt, many others are rapidly disappearing, including many species of frogs and amphibians, some birds, monarch butterflies, and wild orchids.

 “What we are doing is changing the environment by trying to control a lot of these pests and pathogens, often for good reasons,” Monosson said.  “But we’re doing it with toxic chemicals, trying to kill them off.  And so that’s the unnatural part.  We are imposing this sort of unnatural selective pressure, and we’re doing it in a timeframe that imposes a really strong selective pressure.”

Interestingly, a few of the species that quickly evolve to cope with the human chemical environment may also bring with them genes that could prove to be a liability over the long run. For example, some creatures that produce more enzymes to chew up pesticides may be spending so much energy on fighting the poisons, they have less energy to hunt prey.

That does not seem to be a problem with the bedbugs, however, which seem to be quite adept at hunting us down while we sleep.