Bedbugs are here to stay, and thanks to evolution, they are getting stronger every day. When Charles Darwin wrote his classic The Origin of the Species, little did he know that his landmark theory would be applicable in 2015 to the lowly bedbug.
Bedbugs have existed for thousands of years. They are referred to in Ancient Egyptian literature, and the fossil record suggests that they have existed for the past 3,500 years. In 2010, New York City was declared the most bedbug-infested city in America. During that same year, the Centers for Disease Control and Prevention (CDC) and the Environmental Protection Agency (EPA) joined together to publish a statement announcing the resurgence of bedbugs throughout the United States.
So, where have they been, and how did this happen?
In the 1950s, bedbugs were practically eradicated due to the application of highly effective pesticides, including DDT. Now here’s where evolution comes in.
About 15 years ago, bedbugs began a repeat performance due in part to increased travel. More importantly, and more troubling, they have developed a resistance to the chemicals that previously kept them in check.
The most popular pesticide is a class of chemicals extracted from chrysanthemum plants. The chemical is known as pyrethrin, and its synthetic version is called pyrethroid. Pyrethrin probably came about as a way for plants to protect themselves from insects — a great example of evolution via natural selection.
Pyrethrins and pyrethroids work by attacking the nervous system. Bedbugs and humans have small pores in their nerve cells that can be opened and closed to allow sodium passage into cells, resulting in a nerve impulse. These pesticides interfere with the process by binding with the pores, causing them to remain open and allowing sodium to pass unregulated. This causes uncontrolled nerve impulses that ultimately result in paralysis. Our bodies, which are much more biochemically advanced than those of bedbugs, are more efficient in breaking down foreign chemicals, so the damage these pesticides can do to our nervous system is minimal.
What changed in bedbugs to allow them to be unaffected by these pesticides? The answer lies in mutations. Actually, researchers have discovered that a change in just two of the 2,000 amino acids that make up the sodium pore makes a bedbug 250 times more resistant to the most commonly used pyrethroid. The pore is altered just enough that it can function relatively normally in the presence of the pesticide. This means that the bedbug survives the pesticide to pass on the mutation to their offspring and voilà, super bedbugs are born!
Historically, DDT was extensively used on bedbugs. However, due to its environmental and safety problems, its use was abandoned. Similar to pyrethroids, DDT kills insects by a similar action on the pores in nerve cells. During its use, it initiated resistance via natural selection and prepared the bedbugs to quickly evolve resistance to pyrethoids.
To make matters worse, another group of researchers have found that evolution of the bedbug’s outer shell has made it thicker and also increased the enzyme levels involved in metabolizing pyrethoids. This increases the first encounter barrier that physically inhibits the pesticide from reaching the nervous system and degrades the chemical itself via the enzymatic action.
Understanding the mechanisms of action of pesticides and how they become resistant are the first steps in formulating new defenses against them. The CDC and EPA recommend an integrated approach. Integrated pest management is effective and environmentally sensitive. It includes some pesticides, but also includes heat or cold treatment, vacuuming, removal of clutter and sealing of potential entry sites. These techniques are unlikely to generate resistance.
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