Don’t Let the Bedbugs Evolve

New studies of bedbug genes offer the latest supposed example of evolution in action. The Wall Street Journal reports that the “irritating pests . . . are quickly evolving to withstand the pesticides used to combat them.” Alarmingly, the creatures are now able to survive pesticide applications a thousand times greater than what was lethal just a decade ago. In New York City, bedbugs have become an estimated 250 times more resistant to typical pesticides than are bedbugs in Florida.

University of Sheffield bedbug expert Michael Siva-Jothy claims the resistance “has evolved very recently,” while University of Massachusetts toxicologist John Clark argues that “insect resistance is nothing more than sped-up evolution.” But is it so?

One study, conducted by Ohio State University entomologists, focused on the biological process by which bedbugs turn toxic pesticides into harmless substances. Bedbugs exposed to pesticides show substantial genetic “activity” among genes that control the enzymes that catalyze the reactions that break down the pesticides. Another study, conducted at Virginia Tech, showed that genetic changes over time may be increasing the width of the bedbug exoskeleton, helping the bugs keep pesticides out.

Over time, the bedbug population as a whole develops greater resistance to pesticide simply because the bedbugs that survive are all descendants of those that already had greater resistance.

But are these changes actually “evolution”? As in the oft-misrepresented case of microbial resistance to antibiotics, a bait and switch (perhaps inadvertent) takes place: evolution subtly goes from being a synonym for “change” to being a synonym for “progress.” The change in how susceptible bedbugs are to pesticides can be explained entirely as a consequence of selection effects. Starting with an initial bedbug population of high genetic diversity, including some bedbugs with the “right” enzymic processes and others with thicker exoskeletons, treatments of pesticide will decrease the life expectancy and ability to reproduce of those bedbugs that lack the right enzymic processes or thicker exoskeletons. Over time, the bedbug population as a whole develops greater resistance to pesticide simply because the bedbugs that survive are all descendants of those that already had greater resistance.* Mutations may also be involved, but the resistance can be explained by mutations that distort or reduce the bedbugs’ genetic information, rather than mutations that add new information (which have never been observed).

Yes, bedbug populations are changing, apparently in response to increased use of pesticides as they spread. But this change doesn’t provide evidence for progressive genetic changes that lead to new, more sophisticated life-forms.

*It may also be, as we discussed earlier this month on “persistence,” that some of the increased bedbug resistance is another example of a non-genetic biological response to environmental changes. But this response is programmed by already-existing genetic information.