kdr pyrethroid resistance widespread in U.S. bed bug populations

The University of Kentucky announced yesterday that knockdown resistance (kdr-type) mutations, conferring resistance to synthetic pyrethroid pesticides, are widely prevalent in U.S. bed bug populations. The study, forthcoming1 in Archives of Insect Biochemistry and Physiology, finds that one or two of two previously identified genetic mutations (briefly discussed here) are present in a majority of U.S. bed bug populations.

From the press release:

Fang Zhu, a post-doctoral fellow at UK along with fellow UK entomologists Mike Potter, Ken Haynes and Reddy Palli and several students, analyzed 110 bed bug populations from across the United States and found 88 percent of them had one or two genetic mutations. These mutations produce what is known as knockdown resistance, meaning the insecticide is not able to kill bed bugs.


“We need alternative insecticides to fight this bug,” Potter said, “Unfortunately today’s products are not as effective as ones we had previously. Non-chemical measures are important but are seldom completely effective and can be laborious and expensive. History has taught us insecticides are a crucial part of the bed bug solution.”

Data from this study will help pest management professionals make future decisions.

“The methods and primers developed by this group could be used to tell pest control professionals whether or not pyrethroids work on certain bed bugs by looking for these genetic mutations in the bugs’ DNA,” Palli said. “If it’s a target-site mutation, like the majority of these, spraying probably would be ineffective, but if it has another type of resistance, we could possibly add synergists to the current insecticide to help fight them.”

kdr-type mutations cause resistance at the pesticide target site via a mechanism of nerve insensitivity. (For an accessible explanation of pesticide resistance, I refer you to our interview with Dr. Alvaro Romero last year.)

For organochlorines and pyrethroids, these target sites are nerve sodium channels. Thus, DDT resistance can lead to pyrethroid resistance, as both pesticide classes act on the same target site.

As this study is not yet available, I reached out to the University of Kentucky researchers for clarification of the potential meanings of these findings.

New York vs Bed Bugs: Your study shows that the two mutations identified by Yoon et al. (2008) in a NYC population are actually widely prevalent in the United States?

Reddy Palli: Correct, more than 80% of populations showed the presence of one of these mutations.

New York vs Bed Bugs: In the press release you indicate that pest management professionals might use this information to determine a course of action. Can you confirm if UKY’s NYC and Cincinnati bed bug populations are among those with kdr mutations in your study?

Mike Potter: Some of the populations we tested from Cincinnati had one or both mutations while a few others did not (both of the latter still showed high resistance to pyrethroids in bioassays, however, suggesting that other resistance mechanisms may be involved). As far as the NYC populations we tested, all (12) had one or both mutations for pyrethroid resistance.

New York vs Bed Bugs: Are kdr mutations predictive of cross-resistance with other pesticide classes? I note that DDT conferring resistance on modern populations is stated as a possibility (but does this require further investigation?), but what of other possible cross-resistance possibilities?

Reddy Palli: Insecticides (eg. DTT, BHC) that use sodium channel as a target site likely show resistance. As you say, this requires further investigation. Insecticides (eg. Phantom and Propoxur) that work through target sites other than sodium channels may work fine on these resistant populations.

Mike Potter: Unfortunately, we just don’t have too many of these presently that have residual activity as a dry deposit other than products like Phantom (chlorfenapyr), desiccant dusts (e.g., silica gel, DE), and to a degree, the IGRs. Propoxur would be another but the decision to grant it a Section 18 emergency exemption is up to EPA.

New York vs Bed Bugs: I think the public may misinterpret this study as confirmation that “pesticides don’t work” — which is not really the case.

Mike Potter: I think it may be a bit too strong of a statement to conclude that pyrethroids “don’t work” on most of the bed bug populations in US, as we often do kill a percentage of the individuals we test in the laboratory, especially when they are contacted directly with the wet spray deposit. Dry residues typically kill far fewer and we know this to be important for optimal performance of products in the field. Reports from many pest control firms further indicate the pyrethroid products are not performing as well as they would like. Some companies continue to believe that they are working ok, but generally these companies are also incorporating additional treatment measures such as the use of contact killers (Sterifab, Bedlam, Phantom aerosol, etc.), steam, encasement of beds, etc., making it hard to know what specifically is working.


I thank Dr. Palli and Dr. Potter for so kindly taking the time to answer my questions.

This is most definitely bad news; however, we have been expecting as much and indeed researchers at the University of Kentucky have been warning of widespread pyrethroid resistance for years. Having this confirmed, on this scale, is still a blow. The urgency of having options to enable the most basic resistance management countermeasures should be obvious.

Perhaps I should remind you that today is the last day of the public comment period for Ohio’s Section 18 propoxur exemption request under consideration by EPA.

  1. 4/10 – the article has been published: Zhu, Fang, John Wigginton, Alvaro Romero, Ali Moore, Kimberly Ferguson, Roshan Palli, Michael F. Potter, Kenneth F. Haynes, and Subba R. Palli. 2010. Widespread distribution of knockdown resistance mutations in the bed bug, Cimex lectularius (Hemiptera: Cimicidae), populations in the United States. Archives of Insect Biochemistry and Physiology 73, no. 4: 245-257. doi:10.1002/arch.20355. []


  1. sam bryks

    Renee,, as usual you do the scoop as a superb communicator and get the information out before most of us would even know it exists. Great stuff!!! Well done!!!
    It is interesting to get this elegant confirmation of what researchers have been saying for many years.. the fact that it is tough to kill bed bugs with current products.
    We have even fewer products available in Canada, although our Regulatory Agency, PMRA has assigned staff to facilitate a Committee of people from across the country to address this and we hope some of the products currently available in U.S. will be available in Canada..
    Reading the post, Renee, what struck me as key is Dr. Potter’s insightful comment about the fact that the pyrethrins (including synthetics) do work as direct contact insecticides though he does qualify this in terms of other products and actions that facilitate control.
    We had the SPMAO annual conference last week and Jeffrey White of Bed Bug Central was a featured speaker. His insights into the difficulties of control and the necessity of detail of treatment were very familiar. He also gave a different perspective on preparation requirements – that is in some cases, the extent of preparation may not be necessary, but this takes a high end inspection/treatment process that is really not affordable in the non profit housing sector. Although some might consider that failure of control is an even bigger cost, those experienced in this area would advise not to hold your breath till those kinds of services are standard in non profit housing.
    My thought comes back to a sensible approach that emphasizes detail of treatment so that the fast “tricks” are not tolerated. There was some disagreement about whether some form of treatment should be implemented when units are not fully prepared with some including some members of SPMAO taking the position that if the unit is not prepared, then don’t treat, wheras others including myself, take the approach that when a tech is at the door, you can always do SOMETHING useful to start the treatment process even if it is not spraying.. i.e. vacuum them up!!! and spend some time explaining to tenant how important prep is and giving some advice in their specific case so that next week when you come back, the tenant has done something knowing you will be there, and that you took effort to help in the short term as well as explaining why prep is so important..
    Resistance, yes.. but can control be achieved.. I do think so… if you do it carefully and use all the tools available. or at least vacuuming as part of the process. If one can remove a few hundred bed bugs even in a situation in which spraying cannot be done, well, imagine the impact on reducing increase in numbers. and that’s less to kill by spraying.
    Jeffrey also presented great info on reseach on monitors rating the leg protectors as the most cost effective monitor when compared to all others, and it works pretty well..
    The climb ups are a very elegant design, but home made versions will likely work just about as well with a wee bit of ingenuity and at a fraction of the cost.

  2. Renee Corea

    Sam, the fact the pyrethroids mostly work on contact make them no better than soap to borrow the phrase of a medical officer in the 30s. This is far from a saving grace. At least there is no evidence that bed bugs avoid resting on soap. This is a horrible situation.

    I’m glad bed bugs were prominent in your conference. I think the idea of the scorched-earth prep list needs to be reevaluated, but I agree that ultimately the detailed inspections that would make more targeted and reasonable prep possible now only occur in high-end services.

  3. Sam Bryks

    I think we all agree that we need more efficacious products than the synthetic pyrethroids. If it were a fact that most bed bugs sprayed directly with the current products did not die, then i would agree with you that they are no better than WATER, never mind soap, but even against the difficulty of resistrance companies in Canada are achieving control – albeit not easily – when they use all the tools or at least most of them including dust and vacuuming and as appropriate steam treatment. Otherwise, we might as well just stop using the spray products and focus on vacuuming, steam and dust. If indeed, the products still kill by direct contact, then the focus should be on better treatment techniques – more crack and crevice than fan spraying which is still more prevalent for most firms.
    I still come back to a comment by Cornwell, long time Technical Director of Rentokil in Europe the author of a two volume monograph on roaches in the late 60′s who basically said that it is critical to look at treatment technique before ascribing failure of control to resistance as the main cause.
    I have dealt with failure in quality of treatment for 30 years, and it remains a major problem in the industry though it is not usually spoken of openly except perhaps in the encouragement of good practices by NPMA and the trade magazines and associations. Control may be improved with new products other than pyrethrins, but good treatment practices remain a critical element in my view.

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