In the May issue of Pest Management Professional (please see the magazine digital edition here), Alvaro Romero, Michael F. Potter and Kenneth F. Haynes of the University of Kentucky describe a set of initial data on the efficacy of dusts against bed bugs. They tested two pyrethroid-resistant bed bug populations from Cincinnati and New York, one “moderately pyrethroid susceptible” population from Los Angeles, and one of those sheltered Dr. Harlan populations:
We tested five different dusts representing two insecticide categories: two pyrethroid-based dusts, DeltaDust (deltamethrin 0.05 percent) and Tempo 1% Dust (cyfluthrin 1 percent); and three desiccant dusts, Drione (pyrethrins 1 percent, piperonyl butoxide 10 percent, amorphous silica gel 40 percent), MotherEarth D (diatomaceous earth 100 percent), and NIC 325 (limestone 99.5 percent). The efficacy of each product was evaluated by confining adult bed bugs (three replicates of 20 insects) from the respective populations on black filter paper circles treated at label rates (or about 200 mg of dust per cm2). Exposure of bed bugs to the dusts was continuous, and mortality was recorded daily.
Tempo Dust killed all bed bugs within 24 hours, Drione in 72 hours and MotherEarth D (diatomaceous earth) in 10 days:
Tempo Dust killed 100 percent of the bugs from all four populations within 24 hours of exposure — a surprising outcome considering that two of the strains (NY-1 and CIN-1) were highly resistant to pyrethroids formerly administered as liquids. Drione, which includes silica gel, pyrethrins and piperonyl butoxide also produced 100 percent mortality of all populations, although 72 hours were needed to kill all bugs in the two resistant strains from New York and Cincinnati. Variable results occurred with DeltaDust depending on the resistance level of the population. While most bed bugs in the pyrethroid susceptible LA-1 and Fort Dix strains died within 24 hours, more than a week was needed to kill 100 percent of the bugs from the resistant New York strain and two weeks to kill 93 percent from the resistant Cincinnati strain. MotherEarth D (diatomaceous earth) was slower acting than Tempo or Drione, but caused substantial (>90 percent) mortality of susceptible and resistant bed bugs within four days and all bed bugs were dead after 10 days. Mortality was notably lower with limestone-based NIC 325 on all populations tested and did not exceed 50 percent even after 13 days of continuous exposure.
The authors were surprised by the efficacy of the pyrethroid dusts against both resistant and susceptible strains. They discuss possible reasons for this, the modes of action of dusts plus recommendations for PMPs on application and tools; it’s a must read in light of the continued paucity of available information. I will just quote one more thing:
In our lab studies, we have noticed that barely visible deposits still result in an accumulation of dust on the underside of a bed bug, especially toward the rear of the abdomen.
We should note that diatomaceous earth (DE) in particular is very widely used by the public to control bed bug infestations; however, people suffering from bed bugs in their desperation may use DE and other dusts inappropriately, purchase the wrong kind of diatomaceous earth (the pool filter kind), and blanket their homes with DE, which even if it is the right kind (labeled for pest control) can cause respiratory problems if applied incorrectly—the bedbugger faq on DE has safety precautions suggestions. Education is clearly needed but as always the problem of education is reach. Lately I’ve been thinking about the education problem and whenever I’m fully back we should talk about it more.
I look forward to additional findings from researchers trialing dusts and specifically additional work on the effectiveness of various DE formulations, especially with short exposures, anything to help us understand the provocative remarks in Benoit et al. that we recently discussed. I also understood that researchers at Virginia Tech had been conducting tests with dusts. (There definitely should be more instances of researchers sharing information directly with the public—and while we’re at this, making a list for Santa as it were, I really wish research journal articles were open access for the duration of our bed bug troubles. We want to know everything and we want to know it not too long after they know it, is that unreasonable?)
Alvaro Romero was very kind to answer our questions about his research earlier this year.