Friday, August 5, 2016

Comparing dusts for bed bug control

For several years PMPs have known that dusts can be useful tools in the management of bed bugs, but a new paper in the Journal of Economic Entomology by Narinderpal Singh and colleagues at Rutgers University shows just how powerful they can be.

Singh et al. used four different lab assays and two strains of bed bugs to probe the efficacy of eight insecticide dusts.  Each assay showed a different aspect of how these dusts perform.  Together, I think, they do a pretty good job of evaluating how you can reasonably expect these products to perform in the real world.

Four experimental assays used to study the toxicity of
various dusts and predict their effectiveness in the field.
Clockwise from upper left (1) brief exposure assay, (2)
choice assay, (3) assay where CimeXa-treated bugs are
allowed to mingle with untreated bugs, and (4) continual
exposure assay with treated paper . (Singh et al. 2015,
J. Econ. Entomol.)
One of the problems with doing lab assays is that they can be highly unrealistic.  Sure, you can put an insect on a treated surface and watch them until they die (a continuous exposure assay).  Certainly this kind of assay can tell you whether there is potential for a product to work; but in a customer's home do your bed bugs have nothing better to do but sit on the insecticides you put out?  Probably not.

More often than not in the real world, insects run quickly across an insecticide barrier and then spend most of their time resting on untreated surfaces. Insecticide exposure may be only a matter of seconds. At other times, insects that move back to a treated harborage may be able to sense when they are on insecticide residues.  They may then choose to move to a clean spot that has not been sprayed or dusted (a sign of repellency).  Continuous exposure assays may overestimate the effectiveness of insecticide applications, especially when applications do not reach key harborage areas, or when residues are repellent to the pest.

On the flip side, insects may inadvertently pick up insecticide residue from a treated surface and carry that insecticide on their cuticle back to a harborage area. When this occurs they may transfer it via contact to other bed bugs clustered in the same harborage.  Failure to account for this in lab assays might end up underestimating the effectiveness of your treatment.  

Singh and colleagues tried to account for all of these possibilities in their research. One assay required the bugs to sit on treated paper for the length of the study.  A second assay had the bed bugs walk across a treated one-inch barrier.  And a third test gave the bugs the choice to visit and rest on either dust-treated or untreated surfaces.
Bed bug dusts included in the trial were Tempo, DeltaDust, Cynoff, Pyganic, EcoPCO D.X, Alpine, MotherEarth, and CimeXa. 

As you might expect, all products killed bed bugs when they sat continuously on the treated surfaces. After five days there was 100% mortality for all bed bugs in the treated dishes. When bed bugs were allowed to choose freely to rest on either treated and untreated surfaces, CimeXa and Tempo gave 80-95% control after one day; however after 10 days MotherEarth (diatomaceous earth) and Cynoff were close behind.  

The clear champion of the toughest test, the brief exposure test, was CimeXa Dust. CimeXa provided 95-100% mortality (at 1 and 10 days after exposure) to bed bugs crossing a one inch barrier of the dust.  Tempo was the next most effective product in the brief exposure trial, providing 40-60% mortality against the two bed bug strains. This ability to kill bed bugs with very short contact can be a game changer. It suggests that CimeXa may be capable of providing decent barrier protection on bed and furniture legs, in dressers or even along door thresholds (though unprotected deposits will likely be quickly rubbed or swept away). 

Singh and his team then went on to see whether CimeXa might also have the ability to transfer from exposed to unexposed bed bugs. It did. Clean bed bugs, that had not been previously exposed to CimeXa, when placed with CimeXa-treated bugs also had significantly higher (80-100%) mortality after 10 days compared to untreated controls.

Singh's work backs up previous work done by Mike Potter's lab in Kentucky.  Potter's group found that CimeXa was more effective than liquid Temprid residues against resistant bed bug strains in continuous exposure assays. He also found that as a stand alone treatment in infested apartments it provided rapid and marked control, superior to diatomaceous earth, and similar to that provided by the top liquid insecticide sprays. 

What these studies tell me is that insecticide dusts should definitely be part of your bed bug control program, especially in accounts with insecticide resistant bed bugs.  Silica aerogel, the active ingredient in CimeXa, performed better than the other commonly used desiccant (MotherEarth, i.e., diatomaceous earth), and even out performed the other pyrethroid dusts.  It should be noted, however, in settings where harborages can be fully dusted, these other products may still provide good control. And laboratory tests cannot fully duplicate what happens in the field--your real world accounts.

But my real reason to single out this study is that it provides a true low-risk option for bed bug control.  Because the mode of action of desiccant dusts is based on abrading the cuticle of the insect, and not on any mechanism that would potentially affect human health, it's a no-brainer to make these products a mainstay of your dust arsenal.  Used inside furniture, behind drawers and baseboards, in cracks and crevices of bed frames, these products make excellent, safe to use, treatments. Even if heat treatment is your tactic of choice, insecticide dusts can provide a long-term supplemental treatment to kill any bed bugs that might re-infest an apartment, hotel room or other bed room.

If dusts are not an important part of your chemical or heat treatment protocols, you may be missing out on a relatively economical, effective and safe option to improve your success rate against these adaptable and tough-to-kill pests.  

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