For years, we heard very little about bed bugs (Cimex lectularius). Now they are popping up all over, or perhaps we should say “creeping” up. Apartment buildings are infested. Websites report on hotels and motels that have suffered outbreaks. And bed bug control companies are springing to life. Where have all these bed bugs come from?
The simple answer is that pesticides – chiefly pyrethroid insecticides – kept them at bay for a while, but now these insecticides aren’t working any more, and we are paying the price – in blood. A paper published in Scientific Reports in March, 2013 reports on a study that investigated how bed bugs become resistant to insecticides. They are, in short, good at it. Authors Fang Zhu et al. write, “Our data showed that multiple mechanisms involved in pyrethroid resistance … widespread in naturally occurring bed bug populations.”
Development of Insecticide Resistance
In any population, some individuals are better equipped to survive a toxic encounter than others. If the toxin doesn’t kill 100% of the population, those that survive are mostly the tough ones, the ones with a certain degree of natural resistance. If that natural resistance can be passed on to offspring, then the next generation will have a much higher proportion of resistant individuals. With repeated exposure to the toxin over a few generations, susceptible individuals are wiped out and the whole population becomes resistant; the toxin no longer affects them. This is what has happened with bed bugs and pyrethroids.
Other insects have become resistant to insecticides by the same process. Populations of mosquitoes developed resistance to DDT after attempts to control malaria. Lice, fleas and black flies have all become resistant to the insecticides we’ve thrown at them. Agricultural insect pests have become resistant to agricultural chemicals.
Pyrethroid Resistance in Bed Bugs
Zhu et al found that bed bugs develop resistance primarily in their integument, the outside covering of the body. Dr. Subba Palli, co-author of the study, notes that this finding is somewhat novel. Most research on pesticide resistance in insects has studied resistance to ingested toxins. It may not be rare, however, because we haven’t really been looking – “no one looks at integument,” Dr. Palli says, “because no one thinks resistance is there.”
Having resistance mechanisms in the integument is ideal for bedbugs because their feeding habits – sucking blood from people – make it difficult to deliver a poison in something they’d eat. To reach its target, a pesticide must be transported across the integument, so resistance mechanisms to prevent that serve bed bugs well.