Pesticide Resistant Strains of Bed Bugs
I’m an Associate Certified Entomologist and I happened to lay on the science a little thick in this post so if you need help understanding, I’ll be happy to explain further. Just email me with your questions. -Rudy
Over the years bed bugs have gotten increasingly difficult to control due to several factors. (For the Spearhead solution to this resistance see Green Bed Bug Control.) First, our company standard for successful bed bug control is a population of zero. A single live bed bug is unacceptable and considered failure. This in itself is a tall order for an industry in the business of control, not eradication. Some companies with lower standards are okay with leaving “just a few” bed bugs behind but this survival leads to hardier breeds and reinfestation. Second, increased international travel has created in major metropolitan cities “reservoirs” of bed bugs that spread further by mixing with normal domestic travel. This is how bed bugs, traditionally thought of as an urban problem, can make their way to very rural areas. The unfortunate reality of rural America is that the affected persons are very unlikely to find a company experienced or equipped for successful (previously defined as complete eradication) bed bug work. Which brings us to our third problem compounding all others: unsuccessful bed bug treatments will create stronger, more resistant bed bugs. It makes no difference whether it was an unskilled professional or an unskilled do-it-yourselfer. If bed bugs survive, their genetic material will live on and create hardier strains. After decades of using insecticides we often encounter what’s known as KDR mutated bed bugs, especially in urban areas. Now let’s unpack that statement because I need to clarify what that means. KDR stands for Knock Down Resistant, not to be confused with a specific pesticide resistance. A pesticide resistance can be gained through repeated sublethal exposure to a specific pesticide. Kind of like an alcoholic with a high tolerance to liquor.
The analogy I use is: imagine I sprayed a crop with an herbicide that killed all plants under 6 feet tall. Through repeated exposures, I will eventually wipe out all plants under 6 feet. Did what I spray make the plants taller on average? No, it just assured that the survivors that lived on and bred happened to be over 6 feet tall. This mutation is a genetic divergence, in this case a bed bug with a thicker cuticle layer affording more protection from pesticides in general. This “thick skinned” strain is known as a haplotype B KDR-like resistant strain and the normally susceptible strain is named Monheim. The Monheim strain has been laboratory maintained since the 1960’s to give us a valuable comparison of how DNA profiles have changed in bed bugs since then. Very few bed bugs (maybe none) will have the haplotype A gene that allows susceptibility to simple insecticides like diatomaceous earth or pyrethroids. These Monheim strains will eventually be wiped out completely except for laboratory populations. It’s also important to know that bed bugs didn’t likely mutate to survive a specific chemical attack; a process which could take decades. It was more likely the unsuccessful bed bug eradication attempts that created this. The haplotype A bed bugs died easily but there were survivors. Those survivors tended to have both a slightly thicker cuticle and an unskilled person trying to kill them. This meant that, generally, only the thicker skinned bed bugs survived. This is a great example of natural selection. Over time this cuticle just kept growing as the bed bugs with the most over-expressive genes for cuticle protein development continued to breed amongst themselves. How much thicker? About 14 to 16% thicker in current samples and will likely increase.
While this percentage may seem minor, in reality, the effects have been a dramatic resistance to most insecticides. For example: deltamethrin, a common pyrethroid insecticide, has been tested on these strains and needs up to 1500% the legal rate to kill effectively. In general, most pyrethroids are going to see, at minimum, a 50% reduction in efficacy. Abrasive dusts like diatomaceous earth are also less effective since their method of attack is to create tiny cuts in the cuticle. Another factor is that most people applying diatomaceous earth don’t know that bed bugs (and insects in general) have the ability to heal these tiny cuts. Furthermore, a bed bug with an over-expressive gene for cuticle protein development will not only have a thicker cuticle but heal faster. I’ve been to countless homes with dramatic over-applications of store-bought diatomaceous earth where the bed bugs were walking through it like it was nothing for years. The person applying it had taken the advice of people online offering unqualified opinions on things they had no first-hand knowledge of. Regardless of whether they had good intentions, all of these parties share some blame in creating hardier breeds of bed bugs.
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