Bedbugger has been following the fascinating genetic research on bed bugs, a collaboration between the University of Arkansas at Fayetteville’s Insect Genetics Laboratory and Texas A&M’s Center for Urban & Structural Entomology, that illuminates a new perspective on the bed bug resurgence: the possibility that bed bugs were continuously present in the United States throughout the period when they were presumed to have been nearly eradicated.
Present and enjoying well-fed lives in chicken coops across the land.
This research has several interesting components and includes the successful isolation of human DNA from bed bugs, evaluations of pesticide resistance and population genetics.
Texas A&M associate research scientist Dr. James W. Austin was exceedingly kind to answer our questions via email.
Bedbugger: News reports about the research indicate the possibility that bed bugs are spreading or have spread in the past via chickens from breeder houses to poultry workers and to the community, is that correct? How significant a factor could this be in the bed bug resurgence in this country and others? And do New Yorkers, who live in a city of seventy or more viveros need to be concerned that urban live poultry markets may also be a conduit, not just via chickens but also via the business next door (structurally, the markets can be in the ground level of apartment buildings) and its employees and even customers?
James Austin: Yes, we have found significant populations of bed bugs in poultry facilities and given their unique ability to phoretically transfer (hitching rides on other organisms), bed bugs are very likely using alternate hosts (such as chickens) to fulfill their dietary needs. This could be a significant factor in the resurgence of bed bugs globally…not just in the USA. To suggest that all bed bug occurrences have emanated from international travel is unrealistic. There are undoubtedly endemic occurrences that are contributing to the resurgence phenomenon.
As for New Yorkers being concerned about live chicken markets…I would be concerned. You have to put bed bug history into context here. Likely, bed bugs were first associated with bats, moved onto humans that probably dwelled in caves, and then onto poultry. When you look at other Cimicids there is a significant number that have direct relationships to various domestic and wild birds, so it isn’t a stretch to see how bed bugs have utilized chickens (and other galliformes) as their food source.
Bedbugger: You have isolated human DNA from bed bugs. Do bed bugs have the potential of becoming a common and significant forensic indicator? Have they already been used in criminal cases?
James Austin: Bed bugs have tremendous potential for assisting forensic experts in criminal investigations, because unlike other obligate blood feeders both male and female bugs must consume a blood meal prior to molting. Bed bugs won’t stray too far away from their hosts if they are consistently available. This means that if you wanted to link a suspect in a criminal investigation to an exact location, you could get pretty darn close. Besides demonstrating that the recovery of human blood from bed bugs is possible, we have also conducted time course analyses and have demonstrated that we can recover mitochondrial DNA (mtDNA) up to 7 days after feeding and short tandem repeat DNA (or STRs) up to 60 days. This offers a significant time window of opportunity for forensic investigators to possibly recover blood samples from bugs that were in proximity to a location of interest. There were no specific differences between male and females in terms of recovering human DNA. To our knowledge, there has not been a criminal investigation where human DNA recovered from bed bugs has been used, but this offers another view to forensic experts if all the right pieces of the jigsaw puzzle are there.
Bedbugger: What is the relevance of genetic population studies of bed bugs to the issues of pesticide resistance and what are the findings so far?
James Austin: If you contextualize genetics and resistance together an alarming (and not too unfamiliar) picture emerges. Based on our use of both mtDNA and nuclear DNA (nDNA) we find significant variation without population structure and support recency of the whole resurgence phenomenon. In other words, we genetically demonstrate no variation in nDNA (which supports recency of resurgence scenarios) and the lack of population structure with mtDNA suggests rapid movement of populations. Basically, this research supports what a lot of researchers believed was true without supporting it empirically.
Bedbugger: We want to make sure we understand the findings. You tested samples from chicken breeding facilities and also from field collections elsewhere in the U.S., is that correct? The genetic variation and population structure you found point to a) populations of bed bugs surviving over a continuous period (presumably on alternate hosts like the poor chickens), and b) a recent expansion of these bed bug populations. Or can we speak of a single, genetically simple population of bed bugs?
James Austin: Yes…we looked at populations collected from numerous locations in addition to poultry facilities. We employed two classes of genetic markers, mtDNA and nDNA. mtDNA provides a glimpse at the maternal lineage of any successive population since this is maternally inherited. nDNA share both parental contributions so you can at least get some perspective of the paternal input as well. In most cases it encodes more of the genome than the mtDNA and is passed sexually rather than matrilineally. Both genes can coevolve within the same populations at different rates. It takes significantly longer to observe changes in nDNA sequences than in mtDNA sequences.
By applying both to these disjunct populations, we are able to definitely support that bed bug resurgence is more recent (if there was significant variation here you would imply that change was going on and continued to go on for some time) and that the absence of population structure from mtDNA sequences supports large scale mixing of populations (if populations were isolated, you would likely detect geographic correlations with where certain haplotypes (of mtDNA) occur). I think it would be too simplistic to believe that all our bed bug problems originated from a single founding population. If this were so, you would have essentially no mtDNA variation because they would all be related. No…in this case there have been several points of origination and likely mixing of several populations which have culminated into the situation we have at hand.
Bedbugger: And the U.S. bed bug population genetic picture with regard to pesticide resistance? What is a “genetic bottleneck” and what are the implications?
James Austin: While screening multiple populations of bed bugs against various insecticides we have found virtually all populations were 100% resistant to DDT. This is not a surprise given that the first observances of DDT resistance were noted almost 50 years ago. It is a little surprising that they continue to be so completely resistant to DDT. This fact would support a “genetic bottleneck” where DDT susceptible populations were so aggressively challenged to DDT that it wiped them all out…only the highly resistant populations might have survived (a bottleneck), hence the relative freedom we have had from bed bugs for so many years. There are examples from other organisms that demonstrate cross resistance from one insecticide to another insecticide (largely because they have similar modes of action), but this doesn’t seem to be as common in bed bugs that we have evaluated from poultry facilities. Without doubt, we find resistant populations that have been challenged with organophosphates (OPs) and the like, so it is too early to assume anything yet. The bottom line here is that when it comes to treating bed bug infestations, careful lessons learned from cockroach management apply (rotate chemicals, good sanitation, applying push and pull techniques, etc.).
Bedbugger: But that is a tall order when it comes to bed bugs, isn’t it? Rotating chemical classes and push-pull (which, and please correct us if we’re wrong, we understand is a strategy to move insects towards treated surfaces via the use of attractants) is going to be hard because, well, we got nothing at present. Or is there hope in any of these areas? Can their aggregating habits favoring feces-marked locations be turned against them?
James Austin: You are correct in that the strategy of push-pull applications focuses movement to a desired area. However, it doesn’t necessarily mean towards a treated area. It is relatively clear that bed bugs favor warm foci for obvious reasons (if you are an obligate blood feeder, you can only find blood from a warm blooded animal…heat=possible meal). Push and pull techniques might employ non-repellent chemistries and heated target zones (or possibly traps). There is good evidence that bed bugs do prefer harboring in areas where feces is deposited. Studies on C. lectularius and other cimicids appear consistent in that they prefer these areas. Your last inquiry about turning their preferred roosting areas against them is one that you will see a lot more of in the near future.
Bedbugger: Can we hope that bed bugs will one day have the research footprint of termites or other economically important pests?
James Austin: In the short run they very well may already have that footprint. One of the reasons termites get people’s ire up so much is the thought of an unseen invader eating one of their most valued possessions, their home. Like termites, nothing would get my ire up a lot more than being fed on while I sleep or thinking about them on my children. This will take a little time, but I think there will be significant interest in bed bug research in the years to come.
Bedbugger: We want to end with a thought about the chickens. What is being done to alleviate their condition? It pains us to think of chickens suffering bed bug bites. Are current control methods having an effect?
James Austin: Unfortunately, no. Many large-scale poultry producers do not even have entomologists on staff to consider ways to manage resistance in these insects. Until producers change their ways, they are more likely to contribute to the problem than assist with correcting it. Now, to be fair to them, it isn’t their fault either. These insects have been around many, many years and they are doing what they do best, surviving at all costs. So, we needn’t be too alarmed that this has occurred, but we can’t just sit on our duffs hoping for better days either.
Heartfelt thanks to Dr. Austin for his generosity and this wonderful discussion.
Update 9/09/08: North Carolina State University researchers have been awarded a USDA-NRI grant to, ambitiously, use bed bug population genetics to determine the source and movement of bed bugs, within buildings, cities and surrounding areas, and even between countries… and between poultry farms/urban environments, to determine whether poultry farms are important sources of the spread. We look forward to hearing more from the researchers on the project, Warren Booth, Ed Vargo, and Coby Schal.